87 Octane - the answer to idle?!?
 

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.

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?

Gas and warranty
 

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?

Re: Gas and warranty
 

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.