I wanted to post this as soon as possible. The manual says there is an 87 octane minimum - regular and I have been using premium as the fuel door recommends for the last month. Well, today I filled it up with regular and thought I would just take it easy and see what happens. The results were that the idle at stoplights was smoother and the missing that was every 3-5 seconds disappeared completely. I know that some would say I got bad gas possibly but since it was two different stations I fueled at and different pumps the last 6 tankfuls I would have to say that it is fuel grade.

Now I know this is a discussion I started in another thread under the Tech Garage as Fuel Type but I thought that this information needed to be shared here since there are discussions about idle, etc.

I do not know if this will be any problem using 87 octane or if teh missing will totally be gone at morning startups, etc. but I do know that it is smoother running. I also am not sure if there is actual reduced power with the lower grade. Possibly others can try this and see what their results are. I am not saying that engine idle vibration is non existent only that it is reduced and the missing is gone in my case.

WOW, that's a break through!

So, now the question is will it pop / studder on start up in the morning?

Mine does it every morning, it does it in the afternoon after work as well. But not when it's warm.

I bet you get better fuel economy as well on the 87, I'm betting the fuel is detonating too early with premium!

This is interesting!! I think someone should fill up with 87 and dyno thier car.

I don't know about the detonation. I know little about gasoline. I DID read once about only two brands that had BMW certification and what that all meant AND that 2 cycles do not like additives (premium grades) but that is about it. One gentleman posted in the tech garage about the rotary racers using low octane due to rotary faster burn needs and that SLOWER burning premiums were a waste or something like that . I will know more in about a week or so. If this holds true, the RX8 would be even more unique - one of the only sports car choices that use 87 octane! oh, and BTW I was at the dealer today in Fort Myers and notice that someone traded their 2003 350Z in on an RX8. They have it in the front of the dealership with signs, etc. They are making a deal of it I guess! The cars must be selling because all new ones are sitting out front every time I go there. They now have 2 - Black and Blue w/cloth.

Wait a second, I re-read your post. Your car was missing every 3-5 seconds? I haven't had that!

Anyway, let us know if it doesn't studder in the morning!

Rod, my theory has always been that Mazda simply put "Premium" as the recommended because of a few reasons.

1. It won't HURT the engine to run premium
2. To stem critics that would say "not premium" must not be a sports car.
3. To avoid people doing excessive mods to the engine or having people think, heck it's only running regular, there must be TONS of potential left in this engine.

Of course this is my conspiracy theory side of me ;)

I was going to try regular, since gas jumped up in price like crazy I just may do that. Or at least mid-grade.

Wing you could be dead on. I've known people that would not buy a car that didn't require premuim. It was a status thing. They also wouldn't buy a car without leather.

Wing,

Just to clarify (and you may have just got it backwards in an earlier post), the higher the octane (ala premium) the <i>slower</i> the burn, so it would not detonate (burn) as soon as regular.

I've also heard of rotary racecars (SCCA) using regular fuel.

Don't know what it means for the 8, but I'll be curious to hear! :)

I always wondered if paying extra for the premium is a waste on a rotary engine.... if 87 yeilds better combustion and thus better performance, we might as well not use premium then...

are there any harmful side effects of doing this?
anyone?

You've covered it in a nutshell. Without getting too technical, if you don't need it you're simply throwing money away.There are different schools of thought on which way to go with the octane.It is the same unique feature of the rotary that allows it to be perfect for running hydrgen (long cycles)
Note: The Renesis does have a slightly increased compression ratio.

To claify the 3-5 second missing:

When I start the car in the morning it pops and jumps some. Then at idle to and from work (17 miles each way) it lightly jumps while idling at stoplights.

This jumping and or popping disappeared with the use of regular gas - at least for today. I will post more later.

I will also be watching the exhaust tips. THey were really sooty the first 2 weeks and then somewhat better but now with the smoother idle and lack of miss hmm....

we will see.

I ran a full tank of 89 and noticed a slight ping constantly. Took me a while to figure it out. This tank is 93 again and no ping. I don't have any popping or jumping like you though.

Most people that race naturally aspirated rotaries use 87 octane in all their NA race cars apparently from what I have heard the lower the octane the better on NA's, 91+ octane has to be used in the turbocharged rotaries because of the increased compression from the turbocharger, however since the RX-8 is a higher compression and has a lot of changes are you supposed to run 87 or premium? From my experience additives do not differ from the different octanes, they differ from different companies, the companies all use the same gas but then use different additives to make it their brand, the only difference between regular and premium is going to be the octane. I am pretty sure on this but I could be wrong, I didn't go into the family business, (very large fuel distributing company on the west coast). Just me .02 cents.

Also when your idle blips up, is that when your A/C is on? I know on my Miata when I have the A/C on the idle will go up from 800 to 1100rpm every once in awhile. My RX-7 used to do that I think, but I changed the fan relays so both fans are on high all the time.

Originally posted by Wing
I bet you get better fuel economy as well on the 87, I'm betting the fuel is detonating too early with premium!

Higher octane fuel prevents detonation (ignition without spark; aka, knock). Octane allows fuel to be compressed/heated to greater extreemes without detonation (basically, it stabilizes the fuel mixture). This does not mean that the fuel is somehow harder for the spark plugs to ignite -- once it starts to burn, it burns.

Use the grade of fuel the manufacturer suggests. If they suggest using 87 octane, use 87. If they say use 89, use 89. If you go lower than the manufacturer recommends, you risk damage to the engine and will probably lower performance & economy (the ECU will compensate when it detects knock by reducing timing, or by throwing more fuel into the mix). If you go higher than the manufacturer recommends you're just wasting money.

On all past non-turbo rotaries back to when time began, the best gas to use has always been 87 octane and this is what I have always used in my RX-7s. Turbo rotaries have always wanted the highest available octane. On an n/a detonation is a non issue. If you are detonating on an n/a, especially one this new, you have other more pressing problems. Typically a manual will say use "at least" a certain grade of fuel. Just assume that number is the best one unless you have money to burn. If the manual says 87 use 87. If it says 92 don't use 87. Simple enough.

The manual says "at least 87" It also states anything regular from 87-90 or premium 91 octane.

It doesn't mention 93 or 94 either!

Sorry I mixed up the "detonation" in my haste.

This thread got me a little curious, because I, like others, am experiencing the rough idle....so I'm at work and decided to download the manual from MazdaUSA to see what it exactly states:

"Your Mazda will perform best with fuel listed in the table.

Fuel Octane Rating* (Anti-knock index)
Premium unleaded fuel 91 [ (R+M)/2 method] or above (96 RON or above)

*U.S. federal law requires that octane ratings be posted on gasoline station pumps. You may use a regular unleaded fuel with Octane Rating from 87 to 90 (91 to 95 RON) but this will slightly reduce performance. Fuel with a rating lower than 87 octane (91 RON) could cause the emission control system to lose effectiveness. It could also cause engine knocking and serious engine damage."

It clearly states that you will lose performance with gas in the octane range of 87~90 and it clearly recommends 91. Are their different manuals floating around? I will check mine when I get home, but I would tend to believe the one on the web site is most current.

This is what the Manuel Says

Vehicles with catalytic converters or oxygen sensors must use ONLY UNLEADED FUEL,
which will reduce exhaust emissions and keep spark plug fouling to a minimum.
Your Mazda will perform best with fuel listed in the table.

Fuel Octane Rating* (Anti-knock index)
Premium unleaded fuel 91 [ (R+M)/2 method] or above (96 RON or above)


*U.S. federal law requires that octane ratings be posted on gasoline station pumps.
You may use a regular unleaded fuel with Octane Rating from 87 to 90 (91 to 95 RON) but
this will slightly reduce performance.
Fuel with a rating lower than 87 octane (91 RON) could cause the emission control system
to lose effectiveness. It could also cause engine knocking and serious engine damage.

I would likely compromise and run 89 octane and see how it does. I am leery of running 87 octane on the 10:1 compression rotors - 89 would likely give you an extra margin.

The "popping" is a rich misfire from incomplete combustion.

BTW, detonation sounds JUST like popping popcorn under the hood. If you hear it, let off the throttle! But, I just don't see a car with all new and healthy systems (cooling, fuel, spark, etc.) that's not turbocharged running into detonation problems due to fuel grade.

The car will very likely make more power on a lower octane - I doubt it's the "missing" horsepower, however.

Dale

Ok, I don't know anything about compression and less about rotaries really.

So I would like to know why / if 10:1 is high on a rotary but not on a piston engine?

Would using a lower octane Fuel(regular, mid grade) cancel out your warranty if you start having trouble and they find out you have not been using the recommended fuel?

I really doubt it, it's not "REQUIRED" it's recommended.

Now if you used "leaded" fuel, then I could see a problem.

Great advice

In reply:

The manual says Premium recommended but fuel not lower than 87 octane may be used with reduced performance.

I have'nt heard any pinging.

This morning I started the car and it popped about 6-7 times in the garage at first startup still. (like before with premium)

The idle is definitely smoother than before though and there was no miss at the stoplights as before with the premium. I ran it to 7500 on a few shifts and everything was great.

The engine sounds different to I believe. Before it sounded troubled - HA here ya go Rotary Psychic!!!!! It sounds like I had a tune-up.

I know that they put additives in the Premium that are not in the other grades. Check at your stations. You nearly always find on the premium pump with this or that Chevron Clenzit or something lke that - but only on the premium. I was told that those additives are what greatly cause 2 cycle engine performance reduction ie jet skis, etc. I do not know with rotary. The car I just traded in had Premium Required stickers and a warning in the owners manual - Millennia S (miller cycle) Doe the ratoary need the additives? Guess not since it is an option to run the lower grades.

I will continue to keep you updated - so far so good. Others to try and report any difference?

Originally posted by cruzdreamer
Would using a lower octane Fuel(regular, mid grade) cancel out your warranty if you start having trouble and they find out you have not been using the recommended fuel?

That would depend on the problem and how much of a dick your dealership is. :) If the problem you have was caused by the use of a lower fuel grade (ie: detonation screwed the rotor seals), then yes your waranty would be void.

Originally posted by Wing
Ok, I don't know anything about compression and less about rotaries really.

So I would like to know why / if 10:1 is high on a rotary but not on a piston engine?

10:1 isn't super high on a piston engine, but it is a high compression ratio. 9:1 or 9.5:1 isn't uncommon to find either.

Originally posted by Keeper


10:1 isn't super high on a piston engine, but it is a high compression ratio. 9:1 or 9.5:1 isn't uncommon to find either.

Just to put it in perspective, the Mitsu Lancer Evo VIII (with a turbo) has an INSANE compression ratio of 19:1!!!

The Audi A4 I used to own (with the 1.8T engine -- a small turbo) had an 8:1 ratio, if I remember right.

10:1 isn't all that high.

Originally posted by jtimbck2
Just to put it in perspective, the Mitsu Lancer Evo VIII (with a turbo) has an INSANE compression ratio of 19:1!!!Are you sure?!? I thought it ran 19 pounds of boost, not 19:1 compression. Most turbo motors have lower than normal compression, not higher. If that thing is running 19:1 and 19psi, I don't want to be around when one lets go!

Are you sure?!? I thought it ran 19 pounds of boost, not 19:1 compression. Most turbo motors have lower than normal compression, not higher. If that thing is running 19:1 and 19psi, I don't want to be around when one lets go!


No kidding - I thing 19:1 + 19psi would equal one heck of a grenade, useful in the armed forces...

I gotta think it's probably somewhere around 8:1?

So then if 10:1 isn't high, what's with everyone saying 10:1 on the RX-8 is high and should use premium?

My hyundai tiburon was a 2.0L 4 cyl with 140HP (when I bought it) 132 after (hint hint ;) ) and it was 10.1:1 compression, and it ran on REGULAR!

I really think the RX-8 is just spec'd for ass saving, or something. Besides we now know it isn't even 247.

What about the use of gasoline with ethanol? An 89 octane is very common in the midwest.....

Hey again

I just read through and am surprised at some of the replies regarding warranty issues. Using 87 or 89 octane could not possibly void the warranty since it is mentioned as an option (albeit with reduced performance)

It comes down to this. If the engine is running better, the soot disappears. gas mileage goes up, and the missing stops then I beleive there will be no question as to what I will use at least. Right now I can only confirm 2 of these as improved - engine idle (run) and missing (gone) Iwill continue to post.

after reading this thread, I said what the heck and filled up with 87 on my way to work (on my way to work, my gas indicator light turned on). I noticed no difference in performance. About 5 hours later, I started up the car and it did seem to idle a tad bit more smoothly than using premium.

One big thing I noticed is my fuel efficiency dropped bigtime. After driving a mere 40 miles, I was already down a quarter of my tank.. YIKES.. I think this probably was due to me wasting lots of gas testing out the performance. But I'm not yet ruling out the 87 octane factor.

On my last tank I got 250 miles on premium gas before the gas light came on... I drove it smoothly but didn't pay any particular attention to keeping low RPM's (I already passed 600 mile break-in period). Anyway, I don't think I'll reach 200 on this tank before the gas indicator lights up...

Currently my tank is at two notches above half and I've driven only 80 miles since the refill this morning.

I will continue using 87 and keeping close logs of my mileage. Then I will switch back to 92 and do the same. Hopefully I'll have something substantial to report in a few weeks. I'll be filling up every other day with this car. Boy... You'd think this car was Irish :^P

Originally posted by Squidward
Boy... You'd think this car was Irish :^P

LOL! It may be a lush, but it's a hell of lot fun at the party! :D

dude what are u smoking!? Its all in ur head that 87 is gunna help, if you are driving aggressively I would HIGHLY advise to stop because it causes engine damage. After you fill up and have a full tank of fuel do you feel faster? Its just psychological, for optimum performance and to care for your engine's health use PREMIUM for the sake of your rotary!

you're probably right.. :)

but I seriously don't think using 87 will damage my engine in anyway..

unless you can prove otherwise, I'll just continue with my little experiment...

Not a big deal, IMO. Plus, I got 100k extended warranty on this puppy, so as to use it as a daily driver... My real baby will be a a 360 Modena I plan on purchasing in a few years...

The "19:1 compression ratio" (for a gasoline engine) written about several posts back seems VERY high. I thought diesel engines (obviously 'high compression' because of the need to ignite the fuel at the top of the compression stroke) were commonly around 24:1 compression ratio.

its not 19.1:1 its 10.1:1 i think

Originally posted by jtimbck2


Just to put it in perspective, the Mitsu Lancer Evo VIII (with a turbo) has an INSANE compression ratio of 19:1!!!

The Audi A4 I used to own (with the 1.8T engine -- a small turbo) had an 8:1 ratio, if I remember right.

10:1 isn't all that high.

The evo runs under 19psi of boost. The engine has a 8.8:1 compression ratio. This is actually a pretty high compression ratio for a turbocharged car, but that engine is damn solid...

Turbo'd engines generally run with lower compression ratios than an n/a engine, typically 8:1. If you look at turbo/supercharger kits out there, it isn't unusuall to see lower compression pistons in the kit (or in a stage 2 kit or something where you turn things up a notch).

To put things into a bit of perspective, my current car's engine has a compression ratio of 9:1 and requires the use of 91+ octane fuel.

NA rotaries are notorius for loving low octaine gas.. I don't see why the Renesis would be any different. You have to remember that what you thought you knew about cars is prety much out the window then it comes to the rotary.

These posts are taken from the RX-7 forum where this has been talked about to death.

That being said my car runs like poo on 91 octane.. When I first got it I ran it on premium all the time and could not figure out why it felt so different than when I got it. One day I tried 87 and WOW it cleaned the idle right up and gave more power.

Quote: Remember the following is for the 13b engine! I don't know enough about the Renesis yet but it sounds like it's a similar story.

It has been dyno proven that a 13B runs better on 87 oc than on 91 or higher unless the timing has been messed with.

The lower octane resists premature combustion better.

In addition it burns slower across the entire combustion cycle, which produces more power in a NA rotary than higher octane burns (more single sudden bursts at initial firing of the leading plug).

If your car runs better (and you have not messed with the timing) on higher octane than a lower octane gas, check the brand of gas you are using. Chances are that it will have a higher ratio of cleaning agents which is what you are proceiving to be better running. Adding a jug of techron would probably do the same thing.

remember that a NA rotary really can't be comparied to a piston engine with a knock sensor, that really will produce maximum power when high octane gasolines are used. Just too different of a burn cycle.

You want to use LOWER octane gass. In fact, you want to use the LOWEST octane gas possible. The lower the octane, the hotter the flame front, and the cleaner the burn. Higher octane is for high-compression motors that require a slower flame front and more compressability.

The fuel property the octane ratings measure is the ability of the unburnt end gases to spontaneously ignite under the specified test conditions. Within the chemical structure of the fuel is the ability to withstand
pre-flame conditions without decomposing into species that will autoignite before the flame-front arrives. Different reaction mechanisms, occurring at various stages of the pre-flame compression stroke, are responsible for the undesirable, easily-autoignitable, end gases.

and:

If you are already using the proper octane fuel, you will not obtain more power from higher octane fuels. The engine will be already operating at
optimum settings, and a higher octane should have no effect on the management system. Your driveability and fuel economy will remain the same. The higher
octane fuel costs more, so you are just throwing money away. If you are already using a fuel with an octane rating slightly below the optimum, then using a higher octane fuel will cause the engine management system to move to the optimum settings, possibly resulting in both increased power and improved fuel economy. You may be able to change octanes between seasons ( reduce octane in winter ) to obtain the most cost-effective fuel without loss of
driveability.

and:

Once the octane and run-on requirements of the engine are satisfied, increased octane will have
no beneficial effect on the engine. Run-on is the tendency of an engine to continue running after the ignition has been switched off, and is discussed
in more detail in Section 8.2. The quality of gasoline, and the additive package used, would be more likely to affect the rate of engine wear, rather than the octane rating.

And:

If you use a fuel with an octane rating higher than what the engine can use, you are just wasting
money by paying for octane that you can not utilise. The additive packages are matched to the engines using the fuel, for example intake valve deposit
control additive concentrations may be increased in the premium octane grade. If your vehicle does not have a knock sensor, then using a fuel with an
octane rating significantly below the octane requirement of the engine means that the little men with hammers will gleefully pummel your engine to pieces.

Originally posted by jsotelo

The lower octane resists premature combustion better.

In addition it burns slower across the entire combustion cycle, which produces more power in a NA rotary than higher octane burns (more single sudden bursts at initial firing of the leading plug).

Am I reading this right? This is the exact reverse of what I've been reading about octane on the net..

It is commonly said that HIGHER octane burns significantly slower than LOWER octane fuel.

Please clear this one up, somebody? Because I'm majorly confused now.

My dealer told me to use premium. In the past I've always considered this "bunk". Premium is only for doctors with BMWs and money to waste.

I'm now on my 5th tank. The best mileage I've gotten is 16/tank. The lowest MPG is just a bit over 14.

I love the performance but I'm very troubled over the MPG. The 8 should perform near the figures posted on the sticker. At this point I am finding the MPG nowhere near my expectations.

My tailpipes are quite sooty so I hope my post 1k tuneup will make for some impovement.

As for octane, I just filled up, for the first time, with regular unleaded. Regular unleaded is now going for $2.20/gallon here in Los Angeles. Thank you very fu__ing much George Bush!

During the past week I have noticed RPM surging during my early morning starts. This condition is something new. The surging has nothing to do with AC. This is not the "popping" that some have commented on. I have not encountered "popping".

I appreciate having the FORUM as a resource to discuss all the various issues about the 8.

Thanks,
TDS

TDS: my car "surges" if you mean this.

You start it, it jumps up to 2K rpm or so.

It then idles down to 800Rpm and then jumps back up to 2K it does this 2 - 3 times than settles down after a bit.

I'm running premium since day 1. Others have mentioned this on the forum as well.

The Renesis compression ratio is 10:1. All turbo rotary compression ratios since 1989 have been 9:1. In '87-'88 they were 8.5:1. N/a compression ratios after '89 were 9.7:1. Before this they were 9.4:1 until you get back to 1980 and earlier when they were 9.2:1 or 9.4:1 depending on which car it was. Hope that answers the compression ratio questions. Forced induction can be done on high compression engines but boost has to be limited to a lower level, timing can't be too agressive, and higher octane must be used.

Lower octane gas will not hurt your rotary engine. Your compression ratio isn't THAT high. If you ever add forced induction, nitrous, etc, kiss the 87 octane goodbye. 87 octane has worked for 40 years now and will easily continue to work for many more years. Early engines ran off even worse gas than we have now and they were more finicky and less refined than the Renesis.

FWIW: The president is not responsible for your high gas prices. I don't care if he's a Republican, Democrat, or otherwise. The president doesn't have anywhere NEAR the control of what everyone blames them for. It's the damn childish feuding between our 2 biggest scandalous political parties. Come to Texas to see a fantastic example of how not to get anything done. The U.S. has 10 times the amount of oil that the middle east ever had (It also costs more than 10 times more to produce here). Central Africa has even more. If we were to double our current consumption rate of oil (the world) we still wouldn't run out for over 250 years! This also makes some very foolish assumptions. 1) Our consumption rate will never get lower (or higher) 2) We will never find any more oil anywhere else in the world 3) We will always be dependent on oil due to a lack of newer technology. Blame OPEC and the middle east, not YOUR own country. Gotta vote for a proper governor before you can worry about how a president does his job anyways.

Originally posted by Squidward


Am I reading this right? This is the exact reverse of what I've been reading about octane on the net..

It is commonly said that HIGHER octane burns significantly slower than LOWER octane fuel.

Please clear this one up, somebody? Because I'm majorly confused now.


Sorry yeah you read it right BUT he wrote it wrong.. I did a quick cut and paste of a few different posts and this was was WRONG!!!

Okay the lower the octaine the EASIER and FASTER it burns.. Higher octaine burns slower and resists detonation... something you really don't worry about on an NA rotary. The na rotary wants gas to burn as quckly as possible.. This part (from a different poster) was correct.

"You want to use LOWER octane gass. In fact, you want to use the LOWEST octane gas possible. The lower the octane, the hotter the flame front, and the cleaner the burn."

Wanna try to avoid those carbon deposits.

Off the topic.. Do you Renesis guys know about carbon buildup in rotaries and how to avoid it? stolen from atkins rotary so I didn't have to retype it.

1) Never shut the car off before the idle drops off of the enrichment system (choke)

2) Do Tune Ups every 10-12,000 miles and only use NGK Spark Plugs - Change the air & Fuel filters at this time.

3) Unless driving a turbo - use the lowest to mid grade of fuel at a good service station. Here in the Puyallup / Tacoma / Seattle area of Washington state that means Texaco and Chevron. Both of these companies dedicate their expertise in using the min. amount of oxygenate additives and add other chemicals (like Textron) to help the additives burn. If using Supreme or hi octane in a non turbo, the higher octane makes it more difficult to burn all of the fuel allowing for excessive carbon. Turbo or supercharged cars need the slower burning fuels to prevent pinging or knocking which is very hard on the apex seals.

4) Use the BG 44k fuel injection cleaner every 4-6 months (more if all city driving or just short distances- less if mostly freeway miles)

Thanks for tyhe info on the 87 Octane gas. I assume you're going to run a few tankfuls through before determining if it's good for you in the long run. Are you planning on nting the gas mileage as well? it would be interesting to see what impact the change in Octane mught have on fuel mileage.
Again thanks. i look forward to reading your future posts.

I've been using the 93 octane for most of the 2500 miles that I have on the car. I don't have any idle problems BUT the one time that I let my dealer fill up my car, I notice (within minutes) that I had a funny BBRRRRRAAAPPP noise (rotary version of ping?) when I would push the engine to more than 6000 RPM. Once I ran that gas out and filled up with the 93 version, the noise went away. I'm going to try and use the next level down which is 91 octane. I'm hoping that this middle of the road approach will do the trick!

DeBug

okay, here is my first data to report. Not enough time has lapsed yet but some conclusions can be drawn,

My commute is the primary use of the car. It is a 17 mile one way jog through a 4-6 lane road/city driving with several lights - like many towns in FL. The first month - running premium gas I averaged 15.89 mpg and of course I drove fairly easy the first 600 miles. The car sputtered and missed at initial startups and at red lights and there was a definite vibration at idle. The soot on my rear trim area was similar to a diesel car.

I switched gas to 87 octane as per the manual's allowance for such. It took a half tank to notice a difference in the smoothness of the engine. The checked gas mileage at that point - a halftank was 14.5 MPG - YIKES! I filled the tank with 87 and drove it this week. I got gas last night and got 16.29 MPG. Now, considering this is city driving and the fact that I am now using RPM's up to around 7500 - driving it harder than before. I can safely say that I have gained around 1mpg. What is interesting is that the mileage at first shot WAY DOWN.

The engine is running so much better. If the idle were completely smooth (like you hear the engine but don't feel it) I would think I was driving a Huskavarna or a Singer sewing machine. IT is almost as if I am driving amongst slugs - SUVs, work vehicles, big sedans - they are all in the way! oh, and the greatest thing is the little purring sound when you pull it in the garage!!!!! Nice pet car. Nice pet car.

I have similar experiences. I filled up near empty last week at 89 octane, than I drained that tank down to nill almost and fill up again with 89. I'm running purely 89 and the car doesn't sputer on morning starts anymore!

Gas mileage is a little better too it seems! Woohoo, I'm sticking with 87/89.

Thanks fir the input. I hope you'll continue to post after you've run a couple of more tankfulls through. I'm about to switch.

Running a fresh tank of 87 right now, so far so good.

It's pretty wild that this thread is so long. Yet varying observations.

When I picked up my car from the dealer with the full tank of gas, I noticed knocking during the 300+ mile drive home. I filled up with 87 and the knocking continued.

My next tank I got 89. Seems better. No knocking. Yet, I've noticed at idle it doesn't run as smooth and seems to miss once in a while. My old Rx-7 that had a 12a in it -- didn't seem to care what fuel you put in it ... it loved whatever you put in.

I'm gonna try a few tanks of 89 octane and see what happens. I'm curious also to see what impact all of this has on MPG. My drive back from the dealer on 87 octane was right on 24MPG. I don't know that I'm getting that now.

Great thread! Hope all 8 owners get a chance to read it so they can save some $$$ by using regular since the general impression here is that 87 octane isn't so bad after all.

About the MPG calculations, maybe you guys should agree on some sort of standardized method of calculating it to avoid discrepancies/disputes. I've found the most consistent way for me to calculate fuel efficiency was to fill it up and find out how much fuel I used since my last full tank. From my experience most fuel gauges aren't linear.

Excuse me if I'm being knit-picky :D

Even though most of you have already surpassed the 600mi. break-in, the engine could still be going through a break-in cycle and as such, compression will continue to improve over the next few thousand miles.

I just did a performance rebuild of a Cosmo 13B RE for my FD and gas mileage for the first 1000 miles was horrible. I wasn't expecting anything less given the fact it's a single turbo setup. I purposely left the primary runners small to help with low to mid rpm range and fuel consumption. The secondaries are as big as you can go without breaking through the water jacket. Oh wait, I did do that. Gotta love epoxy.

Anyway...at about 1800-2000 miles, I took a trip over to Ft. Lauderdale from Naples. Amazingly, I averaged 24mpg both ways with an average speed of 85mph. Not too shabby! Very little boost of course.

Another thing, the "butt dyno" (depending on how well yours is insulated) needs about a 10hp increase/decrease to notice a difference. If you fill her up with fuel and feel a difference, part of the difference can come from the fact that the fuel is cold, much colder than the fuel that's been circulating in the car for some time. Many circle track racers run "cool cans" which help lower the fuel's temp. The ECU in the FD (third gen RX7) and I'm sure the RX8, takes fuel temps into account.

We all may be in very different climates. I can attest (as can RodsterinFL) that the temps and humidity levels in SW Florida are a bit more extreme than Ohio. Assuming the RX8 has a knock sensor, cold, dense air (relative) would require a bit more octane than the stagnant stuff we breathe down here in the summer. Also, if the RX8 runs very little timing split, it won't benefit much from slower burning gasolines (higher octane) if it doesn't need it. Assuming best performance, the leading timing would be fairly advanced and necessitate the higher octane.

Okay another report -

87 octane is runnin fine.

I checked my mileage again this week and got 16.5 mpg with regular. I have also been reading the Wankel Rotary Engine Book by John Hege and The RX7 by Brian Long. - to get some background on this engine and car

There is also a recently posted thread about disabling the TCS and SCS system and a report of better gas mileage.

I am now convinced that the 13B REW engine we have is fine with regular. --less soot says a lot.

We may end up with a big surprise in MPG!!!!!

I concure, this engine is essentially the same as any other 13B except for the ports being on the side, and having larger ones.

I've been running regular for awhile now (1000Km almost) and no problems, NO sputtering EVER, on reving or on morning startup!

Less soot and MPG is the same or slightly better.

Originally posted by Wing
I concure, this engine is essentially the same as any other 13B except for the ports being on the side, and having larger ones.


This is not entirely true...

The compression ratio on N/A 13B's (FC RX7) is 9.7:1
on the Turbo FC's and the FD it's 9.0:1 (FC for this case refers to 89-91 model, I don't have data on the previous version FC's)

The compression ratio for the Renesis in the '8 is 10.0:1

So it's got higher compression rotors than previous 13B's - intake port location is *not* the only difference.

It could be that they recommend higher octane gas as a bit of insurance against the higher compression rotors.

Although 10:1 vs. 9.7:1 isn't a whole heap more compression, and the NA FC's run just fine on 87 octane (and is what is recommended in the manual).

Simon.

With a 12A Rotary, years ago I was driving through Nebraska on I-80 and filled up with 87 octane. I recall that the pump advertised a higher amount of Ethanol then I later saw in the Colorado winter blend. I ended up getting 30 mpg on that Nebraska tank. Never saw that kind of mpg on a Rotary again. It always stuck with me due to the 30 mpg. I don't remember if it made it sound any different. Give a rotary gas and let it go!

So, what does this all mean? Are the gas companies paying Mazda money to tell us all to use 91 octane? Are we being scammed?

N/A rotary's have allways run better with a lower octane gasoline. Many racers have special low octane gasoline just for racing.

The reason is becuase of the rotarys natural thin combustion chamber. As a result that fuel needs to burn as quick as possible. And lower octane fuel burns faster than higher octane fuel.

The only reason why you would really want to use high octane fuel in a rotary is if you are running a turbo or a super charger. Higher octane fuels also have a higher ignition point, so that way the hot compressed air from the forced induction will not lead to detenation.

Originally posted by hornbm
The only reason why you would really want to use high octane fuel in a rotary is if you are running a turbo or a super charger. Higher octane fuels also have a higher ignition point, so that way the hot compressed air from the forced induction will not lead to detenation.

Or if the chamber compression was high enough to cause detonation. High compression motors (be it piston or rotary) are another reason why you might need to run higher octane gas - turbo/supercharging isn't the only reason.

Perhaps someone at Mazda thought the higher compression rotors in the Renesis might warrant it. Sounds like it's not neccessary though and even though the compression in the Rx-7 is higher than previous 13B motors, it's not enough to require premium gas.

Simon.

Well, after reading about this for awhile, I decided to put in my first tank of 87 octane. Only driven 2 miles on it so far, but so far there hasn't been any unusual noises or feeling from the car.

This may sound crazy, but what you could do is go to a gas station that has parking right next to the pumps. Fill it up, then push it into a parking spot. Go take a walk, do some shopping, come back, start it up, let it idol for a couple minutes. Then try and put some more gas in it. Then I guess you'll see if it eats a lot of gas on startup.

With my two 1st gen RX-7's, they loved gas. I got one down to 10 MPG one time on the way to get new tires (I had to make sure that there wasn't any tred left on the old ones!).

I really enjoy reading your comments. Very interesting!

I have only put 91 in car and will stay that way untill someone provides better proof that 87 is really beneficial

Originally posted by mikeb
I have only put 91 in car and will stay that way untill someone provides better proof that 87 is really beneficial

Right - despite my blatherings on the topic, I also continue run the recommended grade in the owners manual. I'm not willing to take the risk.

Simon.

The way I look at it, the owners manual says 87 is fine, but you may suffer from 'decreased performance'. Well, if I plan on going racing anytime, then I'll fill up on 93. Until then though, I'll be chugging on 87 octane and saving my money for something good ;)

Originally posted by mikeb
I have only put 91 in car and will stay that way untill someone provides better proof that 87 is really beneficial
The benefit would be the price on the pump, what further proof do you need?

I tried the 87 octane right at the 2000 mile mark.

I have not experienced any hesitation or stuttering or anything that feels like detonation. Having once owned a '57 chevy pickup powered by a thrashy 10:1 383, I know what it feels like.

The power doesn't seem like its any more or less than 93 octane. But--it DOES seem "snappier". Slightly better throttle response, although the same power. And the owners manual does in fact say that you can use 87, it's just not "ideal" or whatever.

This is in Houston TX, by the way...plenty hot and humid; if there was a problem I think something would have happened by now.

And yes, for the record, I'm hoping that this means there's plenty of room left for super/turbo charging. :) Yeah, 10:1 shouldn't leave much room, but if it's running on 87....who knows.

all I'm saying is I know 87 is cheaper but the most important thing to me is maintaining my engine and I don't want to use 87 unless their is proof it wont hurt my car.I'll pay for 91 just for the piece of mind

I’m not sure what "proof" would consist of for you or even for me so I decided to experiment based on the fact that 87 was "allowed" in the owner’s manual even though it might not be the best. My car has about 2200 miles and I drive about 1/2 highway and 1/2 country roads where my average speed would be about 50mph :). Let me give you the data on my most recent fill ups.

Octane -> MPG
91 ........ 21.12
91 ........ 20.28
93 ........ 19.67
93 ........ 20.37
91 ........ 21.84
87 ........ 20.57
87 ........ 21.12

Right now I have a tank of 93 in again just to verify that my similar mileage isn’t just because the engine’s continuing to break in. At this point I have a little more than a half tank to go and then I’m going back to 87.

I’d have to agree that with 87 the performance seems a bit snappier - definitely no problems at all with performance being worse – I think it’s better!

At this point I’m convinced that 87’s better so that’s what I’m going to be using from now on – especially with the prices the way they are I feel like I’m throwing money away!

My MPG is definitely improving. While I've only got 1K miles on my RX8, it's getting better and better.

Just filled up last night. Still using nothing but Premium. I'm not brand loyal when it comes to gas since I've never been able to tell the difference in brands with any car I've ever owned over the last 15 years (did find some differences before then, though). So, I always go to the places I can find the cheapest (usually Costco).

All city driving, I got 17.8 MPG....just about where the MSRP says I should be.

For comparison sake....I had a PT Cruiser GT Turbo. I never got over 15 MPG in it using premium...driving all highway. In city driving, it got about 13 MPG....THAT'S IN A 4CYL TURBO CAR. I would bet the SR-T owners are getting about the same.

So do any of you guys trying 87 octane see any difference in the amount of "soot" left on the tailpipes when you use it? Seems like that should improve at least a little, too.

I know that using 87 octane seemed to help Rodster but I haven't noticed much of a difference yet. There's definately still soot but as to whether there's less I can't tell yet. I'll have to wait until I finish my tank of 93 and then I'll go back to using 87 and clean the tips and keep an eye on it.

Since I'm taking the repurchase option, I've got nothing to lose so I started using 87 octane. No differences as far as I can tell. Still getting my 16.9 MPG for 80/20 highway/city driving. I have 2700 miles on the car, btw.

I hadn't thought to clean the tips and see if 87 octane reduces the soot...next time I wash my car, I'll give it a shot and report back. Actually, the thought that all the RX8's seem to universally have this soot on the tailpipes reaffirms my suspicion that the car is just running rich to begin with. Can't wait to hear from companies that start playing around with the fuel system/computer...

okay ANOTHER report

87 octane still

car runs better


I followed the advice of the guy in the other thread about turning off ECS and TCS this week. I went from 16.5 to 18.11 mpg !!!!!! ON the same routes to work this week - another definite improvement.

Remember - this same route in the BMW 328 was 19-20 mpg, in the Millennia S was 17-18 mpg. This mileage is in line with other cars from my experiences anyway considering these two cars were not as performance oriented. (BMW yes but its original 0-60 from BMW was 7.0 sec which they later changed to mid 6's)

I'm still running 89 and well, no sputtering or idle shake.

It really seems to make a difference I averaged 18mpg last tank driving like a mad man, ALL city.

Another tank another week 17.57 mpg based on miles driven from last fill up and amt of fuel.

I'm on my third tank of 87. I don't really notice much difference in power, but the shifter seems to vibrate less harshly. I'm not getting much in fuel economy as it's been about 15.7 mpg over the last couple of tanks for me.

I've been reading this thread with great interest. I will have to try some 87 fuel. However.....anyone have any information on the reason the octane rating (at the pump) for gas at 5000 feet is less than what you find at sea level? Here in Albuquerque 91 is the highest you will find. Does an engine require less octane at higher altitudes?

As for MPG. I now have about 800 miles on the car. The last in town driving fill up I got 17+. Now I either drive too easy or there is something to be said about driving at this altitude. I have seen as high as 19+ when I had some highway miles on that tank, but I don't think I have enough miles on the car to really said what I will end up at. I'll pass along my results with 87 fuel.

BTW I really do enjoy this car. I have never had a vehicle that handles as well as this one. I only wish we had some kind of track in New Mexico where I could push me and the car. That would be such fun!!!

Hmm, something I recently became aware of is that there are different features on the 8's that can effect MPG between models per se. The GT has this DSC/TCS system to disable via the button and others don't. Then there's the auto. (knew that one)

another note (said already) is the RPM econo driving - shift just below 3500 rpm. You really go thru the first 3 gears but supposedly only using one injector. This week my mileage consisted of mainly 10- 17 mile runs to work running the AC on 3 of the runs. Temp was in the mid 70's on 5 runs and in the 90's on 5 runs in humid air. 17.57 mpg with DSC/TSC off

reading the manual, it has list of recommended MPH shifiting points to get the best fuel mileage..

There are two tables, one for regular driving and one for touring I think. They vary VERY little. All points were between 3000-4000 RPM..

I actually tried to abide by that recommendation but I ended up getting UNDER 10mpg.. WTF...... I was so shocked. It seems the HARDER I try at saving gas, lately, the worse the mileage.. Shifting at low RPM's really made it worse..

Going back to my Normal driving (shifting at around 6000rpm with decent acceleration), I get 16-18MPG now.

Anyone experience the same???

Yea...the engine wants to be reved, that's for sure.

I'm getting better MPG partly because I'm through with the break-in miles, but also partly because I'm reving it higher, too I believe.

It seems that cranking up the revs really makes it perform more efficiently

At least that's my story....and I'm sticking to it.

Hmm, so maybe the car is meant to be shifted @ 5k to 6k rpm? Also have people encountered any pinging from the 87 octane? Wouldn't that hurt the engine?

I agree with the engine liking higher RPM. I also notice what others have mentioned - somewhere around 6300 or so, maybe 6500 a surge in power.

This week I drove slightly more aggressively - my mileage dropped from 18.11 to 17.6 mpg - not too big a difference. I now have 2400 miles.

I should top 4500 miles before I turn my car in. I'm at 3800 right now. I've consistently hit 17 MPG throughout the life of the car. Plus, the oil light always comes on at highway cruising speeds. I know there is a fix for this but have not bothered once I had decided to turn the car back in. I do not believe that any harm will come due to the oil light being on. I always check and make sure that I have enough oil.

This will be my last post in this thread.

This week I got gas and obtained 18 mpg. I drove the car much more aggressively than before and ran the AC 2 days (4 trips) on my route.

The only conclusions I can draw are that:

-the car runs fine on 87 octane

-normal driving - shifting at points from 3500 to 5200 or so seem to have little effect on overall MPG

-the car achieves its stated MPG estimate. Something my last two cars did not do.

I would like to thank those of you who posted your results. It was interesting and gave a "norm" per se for those of us wondering about the octane level, idle, soot and of course, MPG.

now the only question is, how is the performance on 87 octane? the problem is that we can't dyno the car, and I have seen articles in car magazines saying that the performance differences between octanes are not noticeable by the 'butt dyno'.

we need that 'speed racer' guy who got the 14.0 sec 1/4 time with his g-tech to try it again after 3 tanks or so of 87!

however, even these preliminary results are enough to make me want to run 87 octane except on autocross days. :)

Okay I said I was not going to post any more here but I finished a study over the past 3 weeks and thought some might like to know that driving habit definitely has an effect on gas mileage.

Some on here have said that you can drive the car any which way and it makes no difference. I found that it does.

About a month ago I was driving the car in town shifting quickly through the gears at about 3500 as my shift point. I consistently got 18 mpg.

So, the last 3 weeks I have driven like a banchee toning out and zoom-zooming all over - great fun BUT the gas mileage dropped to 16.2 - 16.5 mpg.

This goes along with the data on the air intake openings at certain RPM and the fuel injector activation at certain RPM. Obviously if you run one injector (under 3600 rpm) you will use less gas.


I know this contradicts my earlier post regarding rpm and effect but I now have more trials to base my new statement on.
So, on the days you feel like a conservative remember 3500 rpm and on those OTHER days, just have FUN.

this car is fun everyday

I cant help zooming everywhere

Originally posted by mikeb
this car is fun everyday

I cant help zooming everywhere

Yes it's FUN. I don't even figure my MPG anymore. If i'm paying a few bucks more to "drive it like you stole it," then it's well worth it. The chime needs to be heard daily or your not driving this car as it's meant to be driven!

you hit the nail on the head

I've had my car for almost a week and haven't noticed any idling problems or vibrations yet. I have been using 91 [R+M/2] gas and so far everything is ok. In the manual is says the use of 87 can and may reduce performance as well as engine damage and engine knocking. Has anyone here been using 87 octane and nothing else for their car?

Originally posted by skagen
... In the manual is says the use of 87 can and may reduce performance as well as engine damage and engine knocking. ....

It does not! :D

It says:

"You may use a regular unleaded fuel with Octane Rating from 87 to 90 (91 to 95 RON) but this will slightly reduce performance.

Fuel with a rating lower than 87 octane (91 RON) could cause the emission control system
to lose effectiveness. It could also cause engine knocking and serious engine damage. "

Do you see the difference between what the manual says and what you said?

regards,
rx8cited

My bad, you right. So has anyone done any research about which gas causes the idle shaking? Hard to determine myths and truths from the manual and the insight people are posting.

Originally posted by skagen
.... Has anyone here been using 87 octane and nothing else for their car?

hi skagen ,

I forget to say that I've been using Shell 87 without any problems.

regards,
rx8cited

Sorry guys, excuse my noooooobness about gas. used to just always buy regular for my cool integra hehe so I don't know much about the difference between high end gas and regular. In the manual it says in the Anti-Knock index to use 91 (r+m/2) or (96 RON or above). But at the end of the paragraph it says

"Fuel with a rating lower than 87 octane (91 RON) could cause the emission control system to lose effectiveness. IT could also cause engine knocking and serious engine damage."

Is 91 (R+M/2) the same as 91 RON? I've been fueling up at 76 with the highest end gas. I thought that type of gas was 91 (R+m/2).

<-----------------------NOOB :P

Originally posted by skagen
Is 91 (R+M/2) the same as 91 RON? I've been fueling up at 76 with the highest end gas. I thought that type of gas was 91 (R+m/2). No, here in the US gas pumps are labeled with the so-called "Pump Octane Number" (PON) which is the average of the Research Octane Number (RON) and the Motor Octane Number (MON). The MON is always lower than the RON. The manual for North American vehicles refers to the PON which is mathmatically (R+M)/2 where R is the RON and M is the MON.

Usually 91 Pump Octane is about the same as 95 or 96 Research Octane. The rest of the world still uses RON but The US changed to PON for some arcane reason back in the 1970s.

i just run 89 octane here in idaho, piss on that premium shit.

Originally posted by skagen


"Fuel with a rating lower than 87 octane (91 RON) could cause the emission control system to lose effectiveness. IT could also cause engine knocking and serious engine damage."



From what I have read most people that have been using 87 have not had knock. I have not been so lucky My 8's engine has knocked a few times using 87. Only the good stuff for my 8.:)

I wanted to clarify a few things. First, a higher octane gas actually burns SLOWER, not faster, than a lower octane gasoline. Think of gasoline as a MIXTURE of various hydrocarbons with varing burn rates. Parts of a lower octane or "cheaper" gas starts to burn earlier if too much heat is applied. The only reason you would need a higher octane fuel is when you have a higher compression engine. The more squish you have on the fuel under pressure, the more heat is generated potentially causing the fuel to pre-detonate early, before the spark plug even sparked. This is the so-called "pinging" that we hear or hear about. This pre-detonation can hurt power (since it happens too early in the power stroke) and in some instances, can damage an engine.

There are a few other factors that contribute to an engines ability to withstand pre-detonation. Obviously the choice of materials plays a part. In a piston engine, aluminum heads allow for at least an extra point in compression ratio without any ill affects because of aluminum's ability to dissipate heat quickly over cast iron. Other detonation tolerance factors include the amount of spark advance an engine runs, and also what I really wanted to touch upon briefly---Cylinder head design. In piston engines, three basic configurations exist: wedge heads which are, obviously enough, combustion chambers shaped like a wedge with a disadvantagely spaced spark plug; hemi heads with hemispherical combustion chambers with an advantageously, centrally, placed spark plug for more even combustion; and the very compact, efficient pentroof design used on multivalved engines. Now throw all that you just learned about piston engines out the window (almost) and go back and study the rotary engine. It has many inherient advantages over a piston design but not in every area....Where is it's flaw? I'll answer that for ya....It has a very poor combustion chamber design. Study it. It has a very elongated shape and in order to get a full, complete burn, it needs to do so with two spark plugs. Those two spark plugs are there to compensate for this weakness.

Knowing what I just told you about combustion chamber design, do you think a rotary engine needs a SLOWER burning, i.e., higher octane fuel? Combustion needs to start as early as possible. Spark plug number two is just for clean up. Save your money and only run 87 in your engine. The one caveat is if we are running under boost. Otherwise, no need for more. Granted, the extra detergents that better grade fuels have might help here and there to clean your car's fuel injection system but you are really not maintaining anything any better or any worse.

What about a compromise and run 89? Or perhaps run 87 and and every 5th tank full or so run 92 to get the benefits of the extra detergents?

I thought any detonation was really bad for a rotary engine considering how thick an apex seal is. Maybe the lower combusion chamber pressures of the NA rotary helps a bit. To maybe toss in a point, my parents' V6 Accord is rated to run on 87. They get gas at Costco which is the worst gas you can probably buy. It detonates on costco 87 octane, and when I ran some 91 in it and reset the ECU, it still pulled timing quite a bit...

Anyway, if you want to be safe, just run gas from 76 if you life in California. Their octane ratings are spot-on, or better. Chevron is a good brand too, especially if you like keeping your engine clean.

I run 89 and premium once and a while. I have had some rough idling, hesitation ONLY when the engine is not fully warm so am I right to assume it's not because of the gas?

OKay

I went to the dealer about my recent idling issues and was told it was normal. Here, in FL the weather/temp changed and that is the most probable cause _ I am told.

ALSO, NOTE TO ALL OWNERS

The dealer's Mazda senior servicewriter came over when He heard about my idle questions and told me to stop using PREMIUM - that it was causing problems with idle.

As I have said from the beginning, I believe the rotary runs better on regular. I informed him that I learned about the gas grade early on.

Skagen - I have used regular since the beginning of August exclusively. I was experiencing problems using premium with missing and rough idle and soot heavy on the pipes. Since I switched to regular the soot has greatly diminished the idle improved and the missing nearly disappeared - until recently when the temp here in FL dropped down into the 40's or so - the idling got rougher BUT NOTE what the dealer told me to do above.

I HAVE noticed that there is a marked difference in the idle of the engine when cold (very smoth) versus a fully warmed up engine (rougher idle) A fresh tank of cool gas makes the engine idle smoothly too. It seems that the engine is more sensitive to temperatures than other engines - it seems.

i3man - I am not sure that the higher octane detergents are needed. IF regular gas burns better and cleaner in the rotary than the slower burning high octane, that would negate any reason to have the detergents.

Hey Rod,

Thanks for the info man. I appreciate it. I just don't get why the manual says to use premium shit when friggin regular is better for it. Weird. Don't make any sense. Gonna drop by my dealership as well and ask. Thanks again man. Keep ya guys posted on what my dealership says.

Running a higher octane gas every 5 fill-ups MIGHT be a good strategy to gain the benefits of a fuel with some extra detergents. Detergents are tooted as being good for keeping fuel injectors clean and really, it's in dispute how much. If indeed the extra soot or carbon build-up is resulting from higher octane gas---Which I suspect it is, well, then I think I would even second guess the above prevenative maintenance I just suggested. Again, we have to keep in mind we are not talking piston engines, but a rotatary engine with different characteristics.

Also worth mentioning is why did Mazda relocate the exhaust port on this engine from previous years? We know it was emissions related but lets look at it a little closer. Before the advent of fuel injection, this port used to carbon up very badly in it's present position that we have here today in the RX-8. A carburetor just did not have the accuracy back then to precisely meter the amount of fuel this engine needed. Too rich a condition resulted in carbon build up. So Mazada moved the exhaust port where the apex seal sweeps. Good, good, good from the stand point of eliminating the carbon build up from it's original design, but Bad, bad, bad from the standpoint of wearing the apex seal prematurely. Also, the extra overlap resulted in poor emissions from sweeping unburnt fuel out the door and into the atmosphere. Knowing that the rotary engine will never again pass tighter emissions with this compromise, Mazda again rediscovered relocating the exhaust port BACK to it's orginal design debut. Why could they now get away with doing this and not before??? Because we have modern, superior fuel injection systems that precisely meter the exact amount of fuel this engine needs. No unburned fuel means no carbon build up.

However, do you think an engine's computer is smart enough to know what octane level is being put in it? In a word, NO. All an engine has is a knock sensor. If the octane level is too low, audible pinging tells the comptuer to retards spark. That pinging you hear is pre-detonation. The fuel is burning too quickly and too uncontrollably before the spark plug can start timed ignition. What caused this? HEAT.

What happens if the octane level is too high? Do you think the comptuer will be able to compensate? How? There in lies the problem.

Also worth mentioning is that there are alternative fuels that have very high octane levels. Alcohol is one. A normal piston engine running alcohol can run 14:1 compression ratio without detonating. Why? Well, alcohol is just ether with a water molecule attached to it. In essense, you are burning a fuel loaded with water. Why does this effect octane? Because the water molecule allows for alcohol to burn SLOWER than normal gas. Alcohol motors make great power but they suck at gas mileage since half it's fuel composition is water. However, why do they make good power? Alcohol, although it has a slower burn rate, consider that it has a very controlled, concentrated explosion that happens 'ALL AT ONCE'. Gasoline, on the other hand, is a mixture. In order to have burning 'AT ONCE' you have to ensure that all parts of the mixture have the same burn rates. Parts of lower octane gases burn early and other parts later. The charge isn't 'at once'. Not good for any high compression application that will run hotter than normal.

In summary, what I'm saying is given the very elongated combustion chamber of the rotary engine, this engine doesn't need compact combustion. The higher octane characteristicly burns too slow and the ECU has no means to compensate otherwise---Hence, carbon build-up, a rough idle and overall lower performance.

Originally posted by skagen
Hey Rod,

Thanks for the info man. I appreciate it. I just don't get why the manual says to use premium shit when friggin regular is better for it. Weird. Don't make any sense. Gonna drop by my dealership as well and ask. Thanks again man. Keep ya guys posted on what my dealership says.

Don't believe everything you read. Most people on forums, including myself, are not experts on these engines.

The reason the manual suggests the use of higher octane gas in the Renesis than previous 13B rotaries is the compression ratio. The Renesis has a 10:1 compression ratio compared to 9.7:1 for the 13B non-turbo rotary.

Higher compression means more chance of knock/ping/detonation, hence the recommendation.

I'm going to be sticking with 91 octane because I don't want any chance of detonation in the motor. There have been other folks who ran 87 octane who reported (what sounded like) detonation when under heavier loads. That's good enough for me to shy away from it.

Simon.

Originally posted by sferrett
I'm going to be sticking with 91 octane because I don't want any chance of detonation in the motor. There have been other folks who ran 87 octane who reported (what sounded like) detonation when under heavier loads. That's good enough for me to shy away from it.

Simon. Yes, I have heard that sound with 87 octane fuel. The only beneficial effect of the "Tornado" device (yes, I bought one just to get first-hand experience) is that the "marbles rattling in the engine" sound stopped even when burning 87 octane, and it has not returned under any conditions I have encountered since.

I wonder if the tornado was a sufficient intake restriction to alter the air-fuel ratio a little bit, making it less susceptible to detonation? Interesting...

I have a question. Does it matter if you put in 93 and then halfway through, you put 87? For some reason, I remember hearing that you should empty out the gas tank and then fill it up with another octane if you're gonna switch to a different octane? Fact or fiction?

Fiction. We (Navy) mix different grades of jet fuel in our planes all the time with turbines that have much more finicky tastes than a Mazda rotary, and these varying fuels have widely different flash points from each other. If you have half a tank of 91 and half a tank of 87, you've effectively diluted the one half and enriched the other for a tank of 89. Molecules will mix around regardless of octane rating for that particular gasoline.

BTW, FWIW I'm running 89 with no issues or problems whatsoever. It's not as expensive as the 91/93 my old car required and doesn't carry any possible side effects that only a very few have experienced so far on 87 (and I do mean very few). I'm just splitting the difference, and so far things are great. I figure once every 5-7 tanks I'll find a good detergent 91/93 to run just to keep things clean, but in the meantime as others have said there's no point in giving away good money for octane that isn't necessary. Note - this isn't the cheap bastard in me talking but rather a simple matter of chemistry.

Originally posted by JaChTsai
I have a question. Does it matter if you put in 93 and then halfway through, you put 87? For some reason, I remember hearing that you should empty out the gas tank and then fill it up with another octane if you're gonna switch to a different octane? Fact or fiction? I believe that is fiction, but I'm not a petroleum engineer.

Hey, I see you are in Upland. Hi, neighbour!
The Shell station on Mountain Ave. and Eighth St. (next to Home Depot) had pretty good prices today, but they were packed.

Hello everyone,

I believe this info will be alot of help to you

i have a service technician that works here, which worked for Mazda in Japan.

He has top of the line experience with Rotary Engines. He can seriously take apart an engine and put it back together in 2 hours right in front of you... I wish he can get on here and talk to you guys direclty, but his english is not that great..

Anyways he has suggested that for American Rx8 owners to do this..

3/4 of your gas usage, use 87 octane

1/4 of your gas usage use, 93 (premium)

What this means is , lets say you fill up 4 tims a month. Of the 4 times, fill it up 3 times with regular.. on the 4th time, fill it up with premium.

He tells me that rotary is obviously not a piston engine, therefore it doesnt need the prem. gas. Hwoever you use the prem gas to clean out the engine . of course if you fill up only 3 times a month or so forth, try to work out the figrues but thats the general ratio

Be consistent and use the same gas company, hope this helps . I have to tell you that all of us guys here, all do that and we have great mileage and no flooding issues at all

Good luck

Z

one mroe thing, DO NOT USE SYNTHETIC OIL !

[forget it]

relax dude, give people more credit to thinking for themselves..

people who "blindly follow" are just as guilty as those who spread disinformation.

If somebody wants to say something with the intention of helping others, let them say it and leave it to the individual to decide whether or not the advise is legit.

unless you're proclaiming yourself an expert on this stuff, their word is just as good as yours, so chill out.

Here is an article you might find interesting from sindicate writers also known as Click and Clack:


Dear Tom and Ray:


What is the formula on the gas pump all about? (R+M)/2 -- what's the R? What's the M? -- James

Tom: It's all about octane, James. Octane is a hydrocarbon that, when burned in an engine, has a very high resistance to engine knock, or pinging.

Ray: But since it's very expensive, you never actually burn octane in your engine. The gasolines we use contain no octane. The octane rating simply measures how closely a gasoline compares to pure octane in suppressing knock.

Tom: So a fuel rated 93 octane will resist knock and pinging like a mixture that's 93 percent pure octane.

Ray: There are two different methods used to determine the octane rating of a fuel. There's "R," which stands for "research." The research octane number (RON) is determined in a lab with a test engine running at 600 rpm, which represents a low-compression, low-knock situation.

Tom: Then there's "M," for "motor." The motor octane number (MON) uses a test engine, also in a lab, at a higher rpm. That's supposed to represent higher-speed, higher-temperature operation, where knock is more likely.

Ray: Why is the second one called "motor" when it's also, technically, "research"? Done in a lab, too? We have no idea. Why not L+H for "low" and "high"? Or S+F for "slow" and "fast"? Or if it's going to be meaningless, why not S+R for "Siegfried" and "Roy"?

Tom: Anyway, the way they get the number on the pump is by averaging "R" and "M." Or, put mathematically, "(R+M)/2." So, if the RON of a fuel is 93 and the MON is 87, the octane rating you see on the pump is 90.

Ray: And remember, all the octane rating tells you is how much knock protection you get. A higher-than-necessary octane rating doesn't keep your engine cleaner, make the car go any faster, make your engine last longer or keep your hairline from receding. It just costs more. So use only the octane required by your manufacturer to prevent knock, and no more.


© 2003 by Tom and Ray Magliozzi and Doug Berman Distributed by King Features Syndicate, Inc.


--------------------------------------------------------------------------------

Also found this about octane at altitude.

Tom: And what allows you, Bob, to use lower-than-recommended octane is the altitude in Colorado. Up where you live, the air pressure is lower. That means the pressure in the cylinders is lower, too. So by going up 5,000-plus feet in elevation, you've effectively lowered the compression of your engine, and that means you can use lower-octane fuel without making the engine ping.

Ray: At the altitude where you live, 85 octane is the equivalent of 87 octane at sea level. So, by all means, go ahead and use it, Bob. Along with getting winded more easily, it's one of the fringe benefits of living up there in the mountains.

Wow, I wanna know what ferrett said.

so theres no need for 91+ octane on the 8s?

im considering the 89 grade instead of the 87, to be on the safe side.

I usually use 89. I think it's a good compromise (plus I have stage1 - wouldn't go any lower). Once in a while I'll throw some 93 in there, tho.

Originally posted by SCiMMiA
Wow, I wanna know what ferrett said.

nothing outrageous.. he was just sick and tired of hearing people say things he felt was misinformative, and wanted posts like that squelched.

I am so impressed. Plenty of you guys are explaining the technical operation of the rotary & why low octane works on the atmo engines.

Personally, I have been preaching this for years after reading over Curtiss Wright test results from the 70's where they explained the negligable power differences from the lowest octane through to the highest.

The thing to remember is that the rotary engine combusts its fuel in a different manner to a piston engine. Many of you guys are realising this. Again, well done.........

I have run lower octane fuel in all my atmo RX's & high octane in the turbo ones. High octane fuel in a atmo rotary (10:1 compression or not) only helps the petrol station companies bottom line & not your cars.....

REgards

My 8 wouldn't idle when it got below freezing. Talked to my dealer who got up with the area Mazda rep and she (the rep) said to use 87 octane and it worked. No idling problems since. 17mpg city and 20mpg hwy. Also see thread:
http://www.rx8club.com/showthread.php?s=&threadid=18646

I have filled my 3rd and 4th tank with 87 octane now. On my 3rd, I used 87 from Chevron station. On my 4th (current), I used 87 from 76 Station.

BTW, how do you spot when your engine "knocks"? Ever since I had my 8, I always here this "tock" sound in the engine bay while stop at a parking. Finally, I opened the hood and waited for it. To my surprise, it was just the cooling fans activating!

Is there any other way to watch out for a knock? What about from the Tach, does the rpm surge significantly? Please advise.

And last thing... another difference from 91 and 87 is the smell of the exhaust gases. With 91, I always smell unburned fuel. It was like half of the injected fuel just went out without burning at all. With 87, no more funny smells.

my heads about to explode, so confused...

so, should i stick with the 91+ octane that states in the manual OR use the 87 like other fellow rxers???

Wondering how much temperature plays a part in this? In Texas would it make sense to run 87 during the coldest part of the year and 89 during the summer?

Originally posted by Tirxer
my heads about to explode, so confused...

so, should i stick with the 91+ octane that states in the manual OR use the 87 like other fellow rxers???

Why not try it for yourself? I'm happily running with 87 octane. If you don't like it, switch back.

BTW, the manual states: "You may use a regular unleaded fuel with Octane Rating from 87 to 90 (91 to 95 RON) but this will slightly reduce performance."

rx8cited

My dealer in (Earnhardt in AZ) has said to run 87. I have since the 2nd tank I have 2000 miles now. And it has run better at idle with no performance difference.

WOW this thread is still going! To add to the info, the dealer technician told me to use 87 octane gas when I mentioned occasional idle roughness. I told him I already used it.

I don't know about your owner's manual, but mine says explicitly that 90 octane is the lowest to run in the 8. It's a high compression engine and it needs the extra octane. Running high octane in a low compression engine will burn hotter and extended use can reduce engine life. In our 8's, though, the performance of the engine will suffer if you use gas w/ an octane of less than 90, and isn't perfornamce why we bought these cars?!?!?

Killer...Oh good grief, didn't you read the first 8 pages??, Geeez! I think Mazda didn't really know, still don't what exact Octane rating should be used...it was still a new engine when they wrote it.

Also, they changed the flashed the ECU before import so it would burn a richer mixture to pass future emissions standards and that by suggesting higher octane fuel was a way to ensure it would.

I have yet to put higher than 90 octane in it and it has never run or idled rough, the gas mileage depends on how I drive it, it's never got over 16 MPG yet and there are no pings.

Originally posted by Killerking1964
I don't know about your owner's manual, but mine says explicitly that 90 octane is the lowest to run in the 8. It's a high compression engine and it needs the extra octane. Running high octane in a low compression engine will burn hotter and extended use can reduce engine life.

Killerking1964,

Please quote your manual and version - I'm interested in exactly what it says, not your interpretation.

Why is Mazda telling people to use 87 octane if it's bad for the engine? Ummm, they want us to buy a new RX-8 in a few years ...... yeah, that's it :).


In our 8's, though, the performance of the engine will suffer if you use gas w/ an octane of less than 90, and isn't perfornamce why we bought these cars?!?!?

Many of us are quite happy with the perfomance we get with 87 octane, it's cheaper, in some cases the engines run better than 90+ octane, and Mazda says it's okay to use it. Okay, we know you'll blow us away with your high octane fueled RX-8, but that's alright :).

regards,
rx8cited

I checked the manual for you guys, and even contacted our service tech guys, which also own and maintain their own rx8's

They all use 87 octane gas for the reason of Rotary Engine does not reuire a high octane premium fuel

However they use premium fuel once every month or so, to clean up the engine.

From what the say and being one of them is a Rotary expert, I would trust their word. I am also currently using 87 octane and I see no loss of power , and in fact.. I see an increase in mileage..

Good luck guys

z

Originally posted by RX8Z
I checked the manual for you guys, and even contacted our service tech guys, which also own and maintain their own rx8's

They all use 87 octane gas for the reason of Rotary Engine does not reuire a high octane premium fuel

However they use premium fuel once every month or so, to clean up the engine.

From what the say and being one of them is a Rotary expert, I would trust their word. I am also currently using 87 octane and I see no loss of power , and in fact.. I see an increase in mileage..

Good luck guys

z


im trusting your word:cool:

Ok... this analogy isn't totally spot-on, since we're not talking about a Renesis.

But...

I guy I know who runs well in GT3 on a National level, also runs on a shoestring budget. I'm not sure what he's running now, because there were concerns about passing "fuel tests" with oxygenated fuel.

But... for years he ran his full-on Drummond race motors on 87 octane from the local gas station. Had no problems.

Again... not a Renesis (actually as 12-A), but just showing how a highly-tuned rotary can run on low-octane gas.

FWIW...

I been using 93 since i bought my RX, never had a problem, Why i will put cheap stuff in my brand New car?? Is like buying a Brand New house and putting Cheap Paint that will Fade in 3 Months....Now for the experts here, and theres alot of those, 5w-20 oil is the same cheap or expensive? will you put cheap oil in your car just to save a few bucks now and spend alot more later?

Using higher octane fuel than your engine needs to prevent knock makes about as much sense as offering your car salesman a tip. It's just throwing money away and does not benefit your car one bit. But if it makes you feel good...

Started using 87 octane after I had about 1000 miles on the car. 2 full tanks and no problems. MPG increased from 15.3 to about 17. Maybe a little smoother idle, but that could be my imagination.

MPG seems to be improving as the engine wears in too. :)

On my third rotary car since 1985 - always used low octane 87 to 89 gas without performance loss or detonation IMHO. Using high octane in RX-8 at present but considering changing to low octane when car is broken - 5K at least.

Flooded the car once - and one very hard start - shortly after the flood. Driving and starting well now. Hopefully not an ongoing issue.

The only reason I use 91 in the rx8 vs. 87 in the other N/A rotary car is the higher compression that the Renesis engine has vs. the standard 13B from my '90 rx7. If it were the same compression ratio I'd be definately using 87. Given that it's not, then I take the recommendation in the owners manual and use 91.

no issues with the car to date.

Originally posted by RX-jimenez
I been using 93 since i bought my RX, never had a problem, Why i will put cheap stuff in my brand New car?? Is like buying a Brand New house and putting Cheap Paint that will Fade in 3 Months....Now for the experts here, and theres alot of those, 5w-20 oil is the same cheap or expensive? will you put cheap oil in your car just to save a few bucks now and spend alot more later?

Thats a horrible analogy. 87 gas does not equate to cheap paint. Please learn what octane levels mean before you corrupt the minds of some of the new owners here.

I didnt suggest putting 87 octane fuel to save money, god knows If I wanted to save money.. Id buy a Hybrid Fuel Cell car.. Saving $$ is just a side benefit of using 87 octane fuel vs 91+

If you use 93, thats fine.. continue it but I can almost guarantee you that your not doing anything to improve the performance, reliability, or mileage with such high octane fuel. Rotary is not a piston engine, it does not work the same and does not need such high level octane.

but as someone stated here, its a mental issue.. you think cuz you put the highest octane, you think ure feeding it Red Bull juice.. Thats the results of great Marketing

Z

Guys,

I also wanted to suggest to you that though I dont think MAzda did this on purpose, but if you notice in general alot of manufacters tend to always suggest higher octane fuels for your car..

I believe Honda, is probably one of the first makers that specifically designed the new primeline models (Accords..) to use regular (87) fuel..

If you compare to Camry, Maxima.. they all want 91+

I think in the eyes of the car manufacters, its an industry mental standard that a buyer would feel their car is "better" because it uses higher gas..

I know this sounds crazy, but im telling you.. it works. Do you know how many times, I tell people.. oh the 6 speed accord coupe, all it needs is 87. and they say" Wow it must be slow then.

After a demo test drive, they realize thats obviously not the case..

my cynicism leads me to the following unvalidated, biased, but probably true criticism:

car companies conspire with oil companies to milk consumers

true or not true?

I don't believe there is conspiracy amongst these groups; obviously they are both about profit. If that were the case for example, they would encourage more oil changes and not suggest that everything is rosey stretching to 7500miles.
The auto manufacturers are often struggling to stay afloat, far less make a profit in this current world economy. They both have their strategies for money making and are influenced by many factors including world and market specific environmental concerns. They must communicate and co-operate; but conspire?

Originally posted by RX8Z
Guys,

I also wanted to suggest to you that though I dont think MAzda did this on purpose, but if you notice in general alot of manufacters tend to always suggest higher octane fuels for your car..

I believe Honda, is probably one of the first makers that specifically designed the new primeline models (Accords..) to use regular (87) fuel..

If you compare to Camry, Maxima.. they all want 91+

I think in the eyes of the car manufacters, its an industry mental standard that a buyer would feel their car is "better" because it uses higher gas..

I know this sounds crazy, but im telling you.. it works. Do you know how many times, I tell people.. oh the 6 speed accord coupe, all it needs is 87. and they say" Wow it must be slow then.

After a demo test drive, they realize thats obviously not the case..

Umm...my family has had 3 generations of camry's, none of them suggest premium, only regular. As we leave the lot, the dealer even tells us, don't put premium, regular is actually better for camry engines. Honda accord, the new one, I went Honda about a year ago to look at the new two door accord, dealer says regular gas works just fine and so does the sticker.

By the way putting regular gas it doesn't affect performance instantly. The question is whether or not it'll affect your engine in the long run. That's like saying if I eat a Carl's Jr. double bacon cheeseburger today, I'm gonna feel like crap. No, it only happens after years of eating that shit, and you have a heart attack later. Same thing, just cuz you put regular gas a couple of times doesn't mean you feel a performance change right away, it'll take some time for residue build up to take place. The question is, does that happen to a rotary engine with just regular gas?

Originally posted by skagen
...The question is, does that happen to a rotary engine with just regular gas?

Exactly ........ show me the scientific evidence ........ otherwise its just hearsay.

I am currently using 89 myself. I was using 91 previously but feel it is overkill as well, especially when the car is blatantly running too rich. Last thing I need is for slower burning petrol. I should probably drop down to 87.

I was reading an article on using lower then recommended octane and the engine retards the ignition to handle the lower octance hence the reduced performance. However he went on to say if the retarding(?) system should fail you could have major engine damage happen to your car from detonation. I am not sure if this applies to our cars but wanted to offer this info.

ok....I know someone stated somethin' about mixin' fuels in between fill ups, like 89 w/ 93 in the same tank, that navy dude is right, doesn't matter! and heres proof! --- http://www.globemegawheels.com/news/20030828/Automotive.html should be some help to some of ya's...
I have this link somewhere else in this club, but w/e, here it is again!

as far as this thread goes, I could care less if it goes on forever, thats what its here for. we want to treat the 8's right! as far as stateing whats in the manual numerous times, thats NOT nessacary!!! geesh, once or twice is fine

Here in Spain I can only buy (unleaded types) 95 and 98. I use 95 without problems, although the car is very new (2000km). If anyone knows different....??????? Is the 89 or 87 octane which people talk about unleaded?? Should the car have unleaded or is regular ok??????? Should I try to find if there is 87 and whether it is unleaded????

Hey Paul,
I believe Europe measures Octane differently than US. I believe Europe uses RON method of measuring Octane. 87 US Octane is 91 RON Octane (reading from the US manual). I believe if you read more of this thread you will find more detail. If you agree with the discussion points in this thread where 87 Octane is OK, then 95 RON Octane should be just fine. We are all talking about unleaded fuel. In fact, I believe it is very difficult, if not impossible, to find leaded fuel in the US.

dag

Originally posted by rx8cited
Exactly ........ show me the scientific evidence ........ otherwise its just hearsay.

If youre waiting for someone to document a full analysis on performance, mileage and longetivity.. keep waiting, by that time.. they'll be a new Rx generation..

Many owners including myself, use 87 octane.

Our Rx8 expert mechanic here at the dealership who worked for Mazda and trained my Mazda in Japan, will tell you the same that 87 octane is all you need for the Renesis Engine.

Im not telling you to take my word for the hell of it, but there would be no reason for me to lie to you.

If you put 91+ , then so be it. But if a Rotary expert tells me that high octane fuel is not needed, then I'll take his word for it ..

Z

Originally posted by RX8Z

quote:Originally posted by rx8cited
Exactly ........ show me the scientific evidence ........ otherwise its just hearsay.

If youre waiting for someone to document a full analysis on performance, mileage and longetivity.. keep waiting, by that time.. they'll be a new Rx generation..

Many owners including myself, use 87 octane.

Our Rx8 expert mechanic here at the dealership who worked for Mazda and trained my Mazda in Japan, will tell you the same that 87 octane is all you need for the Renesis Engine.

Im not telling you to take my word for the hell of it, but there would be no reason for me to lie to you.

If you put 91+ , then so be it. But if a Rotary expert tells me that high octane fuel is not needed, then I'll take his word for it ..

Z

I'm not sure what why you're quoted me. ....... I use 87 octane! :D

rx8cited

I used 91 octane since I bought the car last December, after reading this thread I used 87 octane the last few tank fulls and averaged 2 mpg better than I have using the 91 octane! Strictly city stoplight to stoplight driving netted me 14 mpg using 91, the last few tanks of 87 averaged 17 mpg! I did not notice a reduction in power but the timing has to be affected by different octanes. The only time I notice power variations is during a big temperature change per say 50 degrees at night to near 80 during the day!

I dont remember =) anyways, 87 all the way..

So, should I start using 87 in my 2 year old Camry too?

Originally posted by rx8rookie
So, should I start using 87 in my 2 year old Camry too?

If it's a 4-cyl, yes use 87. If it's a V6, I suggest you stick with 91. Toyota engines are dependable. You should not have any issues regarding the use of 87 or 91.

Originally posted by rx8rookie
So, should I start using 87 in my 2 year old Camry too?

What does Toyota recommend for your car and what do you use?

Just found out that where I live we only get 85 Octane. Blimey!

well i'm going to make the switch because my car has the exact same type of idle as originally posted....AND it stalled at a traffic light once.