I seem to have noticed my 8 runs better on 91 octane when compared to 93 octane. This is a seat of the pants thing, but what I really want to know is can I run 89 octane? My gas mileage seems to be better (tested two tanks of each) with 91 octane (avg 19mpg) vs 93 octane (avg 16mpg), but I can't really say if it is better because the weather has been cooler or I've been driving a little more highway, etc. I've read on this forum that rotaries run cooler with lower octane, maybe that is what accounts for the differences, I dunno but I'd like to see what happens with the lowest octane that is "safe" for the engine.

TIA,

Alex

Before you are set on fire by the search-nazi's here, I'll say check your user manual. I cannot remember for certain, but I think 89 is too low.

I ran a tank of 87 without any problems. It was during the gas-crisis after Katrina and after waiting an hour to get into the station all they had was 87. And I was empty.

According to the manual, 87 is acceptable. Mine runs fine on 87. Some others don't.

I bought mine the end of June last year. Followed the recomendations and used premium, until it jumped up to around $3.60/gal. Seeing as how both my rx7s ran just fine on 87, I tried first 89, then 87, and have been running 87 for months now. Car runs just fine.

87 is perfectly fine. An NA tuned Renesis, by Mazsport, has also reflected it is the best for power.

I started mine on 93, then backed off to 89...I'm at 22,000 miles and have run the car on 87 for the past 8,000 with no issues whatsoever.

I too started at 93 octane, but I have backed it down to 87 for the last year.....the only difference is that I am saving some cash.

nother 87 proponent here. Been running 87 for 15k miles, no problems at all and smooth as butta.

Increasing octane did absolutely nothing for fuel economy or performance.

the RX-8 ECU is smart enough to adjust ignition time to account for different octane fuels... so *GOOD* 87 (eg not from those super cheap cash-only gas stations) should be fine

Yeah, I run shell "v-power" 87 pretty much exclusively.

Yeah, like ZoomZoomH said, cars nowadays are smart enough to know when it's detonating. There's this neat little thing called a knock sensor...
Anyways, i dunno about getting more power with 87 octane like RedDevil said... but lower octane means retarded timing... which means reduced performance.
But wait, does a Renesis have timing? OMG wow... I actually never thought about that. ^^

Yes, it has timing, silly. You think the spark plugs just shoot off randomly, lol

of course Renesis have timing, wtf :p:

I've been buying 93, wishing there was a mid-grade 91, but instead it is 89. But after the advice to run it at 87, WOW, that will save me $$$ - thanks all! :rock:

Can anyone help to define ***good*** gas? I always shop price, am I being stupid?

dude, you only save like $2-3 per tank when using 87 instead of 91+, so for most people, it's, what, like $15 a month saving in gas cost? is the 'risk' of putting in low quality 87 worth that $15??

yeah, but that adds up to like $124 pear year! :p

heh...if the difference of $2-3 per tank is making that big of a difference, then perhaps a more fuel economic car is more suitable... ;)

The "risk" ? What risk?

I've had plenty of people here tell me to use 87. I've had my dealer REQUEST that I use 87 over higher octane fuels to avoid carbon deposit build ups. I've read detailed articles explaining why running 87 in a rotary creates a hotter flame front. An article even referenced a discussion with an engine designer from Hiroshima where the car was built, and HE said to run 87 3 out of 4 tanks with the 4th just being for the cleaning additives. I've been running 87 for 15,000 miles with zero engine trouble.

Unless someone can quantify a real risk, I'll take my $2, better mileages, and smoother running that I get with 87 octane. :)

Ok, true enough Zoom ZoomH, but what is considered "quality"? I mean I cannnot tell the difference, I really doubt price is it...are you saying that quality = higher octane? I can live with that. But I think quality may be getting confused with brands.

Asheville has lots of BP stations - good? How about Hot Spot? Enmark? Please don't make me shop at Exxon/Mobil - my visit to the Prince William Sound in Alaska made me swear off their products. So far I have only fed it with 93 octane, nothing too good for my baby, ya know?

The "risk" ? What risk?

the 'risk' is putting in 87 that is so poor in quality that it is actually an 85 (or lower) in octane rating, hello detonation!

even poor quality 91+ will be at least 89 or so, which is well within the 'OK' fuel octane range for the RX-8

and tominavl, basically to me, a 'quality' gasoline would come from a gas station that is well kept, hopefully a well known regional/national brand, and that prices are not RIDICULOUSLY cheaper than competitors in the area.

BP, Shell, etc...basically I think he means to stick with the name brands and away from the unaffiliated or small company, like Joe's Garage, Gas and Gum.

As for the 87 providing more power. I can't prove that nor would I claim to see a difference between 87 and 93 in my car. The Mazsport car was ECU tuned and Scott claimed 87 provided the best power while even costing less. I'm inclined to trust Scott so there's where my statement came from.

The Mazsport car was ECU tuned

that's the key right there, Mazsport car was ECU TUNED FOR 87 OCTANE, huge difference this makes....

I believe STOCK ECU is tuned for best performance using 91+ octane.....

^^^
won't argue with that

The "risk" ? What risk?

I've had plenty of people here tell me to use 87. I've had my dealer REQUEST that I use 87 over higher octane fuels to avoid carbon deposit build ups. I've read detailed articles explaining why running 87 in a rotary creates a hotter flame front. An article even referenced a discussion with an engine designer from Hiroshima where the car was built, and HE said to run 87 3 out of 4 tanks with the 4th just being for the cleaning additives. I've been running 87 for 15,000 miles with zero engine trouble.

and that right there completely counter's any credibitily he might have. cleaning additives are the same for each octane grade (within a given brand).

Just use 98 octane like me, then you dont need to worry at all :bluesuit: I cant believe you guys moan about petrol prices over there.... here in the UK it costs me £60 to fill my tank. You got it eeeeeasy!! :banghead:

to head off the questions about 98 octane...that's 98 RON, which is equivilent to 92/93 octane here in the states.

I use 91 in my 8 and it runs great.
The wife put in 87 from the same station and it knocked like a bunch of vacumn cleaner salesman at the front door. It was a bad sound.
But it was summer here in Arizona and probably about 110 degrees.
That I feel plays a big part in the octane used.
All I know is that I will never put anything under 91 octane in my car here in AZ.
By the way I use QT gas which is a "Top Tier" according to BMW and Honda.

to head off the questions about 98 octane...that's 98 RON, which is equivilent to 92/93 octane here in the states.More like 94-95.

Just remember that the renesis is prone to carbon buildup. Most of the higher octane fuels have extra additives and detergents to clean you combustion chambers and plugs etc to prevent this build up.I feel that the extra expense for this feature alone is well worth it.
Regards
Rexi

Thanks to everybody who responded, for me it is not a money issue, the car just seems to run better (seat of the pants meter) on 91 vs 93 octane. I'll try the 89, and see how it goes. To all the 87 octane people, what is your avg gas mileage?

TIA,

Alex

http://www.rx8club.com/showthread.php?t=22681&highlight=octane

Read the 3rd and 4th posting from the above thread....by MazdaManiac and Rotarygod.

Where are you guys from tha has 93 octane at the pump.Here in cali the highest is 91.Also what the highest octane you run without engine damage or execeve wear.I want to know for when I take it to the track and would it help

I have run 87 octane a couple of times in the car and it gets "slightly" better gas mileage than with the higher octanes, but I can definitely tell that there is a power loss between 91 and 87, harder shifting, and more engine vibration. I can even tell the difference between 89 and 91. Maybe it is just my imagination, but I don't think so. I have one of the early build dates. Possibly that is why. I run 89 when I am feeling cheap and 91 when I am feeling sporty. Average between the two is just under 18mpg.

And remember, if you are concerned about carbon build-up in the engine...rev it every now and then to the beep.

I use 91 in my 8 and it runs great.
The wife put in 87 from the same station and it knocked like a bunch of vacumn cleaner salesman at the front door. It was a bad sound.
But it was summer here in Arizona and probably about 110 degrees.
That I feel plays a big part in the octane used.
All I know is that I will never put anything under 91 octane in my car here in AZ.
By the way I use QT gas which is a "Top Tier" according to BMW and Honda.

I was running QT when I lived there as well. I went down to the 89 and never had any difference. Even ran 87 from time-time. In the summer when they kick into the blend then definetly I would run the 91 but once they change over then you should be fine with 89 or so. But I miss the AZ year round climate!! :rock:

I think one of the only problems is excessive carbon build up from running lower octane

to put things into persepective, i've been running on 89 octane with a cz tuned to 13.0:1 afr and upwards of 6 additional degrees of ignition advance for 1.5 years now without a problem

Well, I have officially changed my tune on this subject. Replaced plugs this weekend. Based on the condition of the plugs (2 years, 14,000 miles) I would say that higher octane is warranted, at least in my case.

and what is the condition of your old plugs that led you to this new assessment??

I think one of the only problems is excessive carbon build up from running lower octane

This should be quite the opposite, the lower octane will "explode" and burn faster for a more complete burn. The 93 octane will actually burn slower and if the rotary is not able to get a complete burn there is where your carbon buildup will come from.

This should be quite the opposite, the lower octane will "explode" and burn faster for a more complete burn. The 93 octane will actually burn slower and if the rotary is not able to get a complete burn there is where your carbon buildup will come from.

yeah but doesn't that only matter engines that aren't high compresion?

High octane is more likely to cause carbon build up. More so than lower octane. Low octane (assuming the ECU is OK with it) should give you better gas milage, more power and less carbon buildup.

Cars that are tuned to high octane can compress what's injected into the combustion chamber further without preignition, giving you more power. Where the RX8 falls out between these two choices I have no idea.

Although it would be interesting to reset the ECU and run it on both types of gas. I know when I did I saw zero difference between the three tanks of gas of low and high octane. The only real difference I've ever seen was running nonoxy fuels vs. oxygenated fuels. The nonoxy was a considerable boost, and an additional 2 - 3 mpg more.

and what is the condition of your old plugs that led you to this new assessment??

Spalling of the center insulator nose; a classic sign of detonation. I found this condition on both leading plugs; although the one in this pic was the worse. The ground electrode was intact but I removed it for the pic.

The car was running ok for the most part but had developed a mild stumble in stop-and-go traffic. It's running smoothly again now on the new plugs. My ghetto compression test (coasting down a long, steep hill nearby in 2nd gear) yields the same terminal velocity of 34 mph that it always has.

87 octane here for 43k miles. and my car was the one that scott at mazsport beat up.

about every 15k miles i run a can of b&g 44k in the tank.

my plugs were like ass a 30k miles. replaced free....

btw. my mpg average is over 21 mpg.

beers :beer:

yeah but doesn't that only matter engines that aren't high compresion?

No that is the nature of gasoline, not the motor. All octane does is make gasoline more stable at higher compression and heat, which in turns means it will burn slower, the higher the octane. If you have a low compression car then you have no need for slower burning fuel (high octane). Some people's 8's run just fine on the lower octane (mine does) and gets better gas mileage than if I use 93, but others have problems using the lower stuff, just depends on the car. Remember also that the combustion chamber of a rotary is much different than a piston engine, so 10:1 on a piston engine seems to be a little different than 10:1 on a rotary, and I think it has to do with the shape of the chambers. Someone correct me if I am wrong.

Ok you guys are waisting your time and actually doing more damage by running higher octane fuel in a NA rotary. Some of you just don't understand how thermally unefficient the rotary is when it comes to fully burning the fuel air mixture. All higher octane gas does is burn slower. The slower burning process decreases the chances for detonation/knock. The side effect is the remaining unburned fuel turns into even more carbon deposits. More carbon just lowers your compression because the internal seals will start to stick. Why do you guys think you keep flooding so much? Flooding is a direct result of carbon infested engines.

Stop worrying about detonation so much. The Renesis is NA. Detonation on a NA rotary isn't know where near as bad as detonation on a boosted rotary. Between the two, there is a huge difference between the internal combustion pressures/detonation events inside the engine. There are guys running PP NA rotaries making 300 hp and running 87 octane. I personally run 89 octane in my Fd which is boosted and it has 103,000 miles on the original engine. You have nothing to fear. Ideally what you want to do is run the the fastest/cleanest burning fuel you can in a NA rotary. 87 octane burns faster and most importantly MORE FULLY. This is what the Renesis needs.

That sums it up. The Engineers at Mazda have no idea what they are doing. :yelrotflm

That sums it up. The Engineers at Mazda have no idea what they are doing. :yelrotflm

No, they do know what they are doing, they know how to market a sports car that is all. Recommending Premium fuel is a marketing strategy now-a-days where if you have to put premium in the tank it must be better. Notice Mazda "recommends" premium, they do not "require" it.

It has also been said over and over some 8's love the 87 and some hate it and love 93. My suggestion is try 87 and if the car runs good on it (mine likes it more than 93) then run it, if not go back to premium.

One last point, at least with my car, it feel much better on 87 than on 93, but putting a bottle of Techron in it every so often makes it idle so much smoother for some reason, and it is only with the Techron additive.

i ran with a few tanks of 89. I feel no difference from 93 but psychologically I still worried about running 89 in the long run.

Sorry about shouting, but shit... I filled up with 87 octane, to see how the car would run. As soon as I hit 5Krpms the engine rattled (very ugly sound) and lost power. I kept the rpms below 4K and went staight to Discount Auto Parts, to pick up octane booster. After I added the octane boost the car ran better but still rattled at 5Krpm.
After I used 1/2 a tank (running at 4k or less), I filled up with 93 octane and the car is fine now. The gas was Shell (both the 87 and 93). The car runs fine with 91, and 89 seems OK, but for now, at least with my 8, 87 is just plain evil.

Cheers,

Alex :mad:

I ran mine on 93 for the first 10K. Since I figured the computer had learned on 93, I slowly backed it off to 87. Now at 22K, and for the last 12K, my car has run fine on 87. Maybe try it gradually.

Where are you guys from tha has 93 octane at the pump.Here in cali the highest is 91.Also what the highest octane you run without engine damage or execeve wear.I want to know for when I take it to the track and would it help

That is not true. I was in Los Angeles for 2 weeks last year and put 93 in my car at 3 different gas stations.

That is not true. I was in Los Angeles for 2 weeks last year and put 93 in my car at 3 different gas stations.

California 91-octane is a result of agreements between the CA refiners and the owners of the gasoline pipelines, partly due to CA regulations regarding reformulated gasolines and removal of MTBE. Any CA gas (except aviation gasoline) that's travelled through a pipeline is max 91 octane, as far as I know. This even affects Nevada, which gets their gasoline piped in from CA. I guess it's possible that a local refinery could supply a small area with higher octane.

When you discuss octane numbers you should also mention weather conditions. Especially temperature.

The same engine will perform well with 87 octane, during the Alaska-winter, but could have issues with 93 octane in Las Vegas during the summer.

guys octane is not a rating of how fast the fuel burns. high octane does not equal slower burn speeds while low octane means faster burn speeds. octane is the measurement of how stable the fuel is to automatic ignition. also most engines generally are less prone to detonation the FASTER the fuel burns. engines now are designed to burn the fuel faster and in doing so have reduced how prone the engine is to detonation. part of it is how the fuel burns. slower burning fuels leave more time for perssure buildup and heat to autoignite the fuel. where if your running a "fast burn" designed combustion chamber you can run less timing make just as much if not more power and use higher compression ratio's. the faster burn when ignited burns quicker and more uniform and has less chance to create two flame fronts or other issues.


read up on it a little more you might understand it a little better but octane doesn't mean slower burning fuel.

So is it ok to put 87 in my car or not? I live in MN and gas prices are starting to rise. I have a 2005 RX8 with 6 speed manual. Ive been putting in 91, but would like to start to use 87. After reading all the words on this post, im a bit weary, but money is crunching. Will it hurt the engine at all or no? I just need a simple answer :)

As always, lots of bad "science" in this thread.
Lots of misconceptions, hysteria and nonsense.

I won't bother to wake any of you from your slumber again. You know where to go for the answers.

Remember (as always):


Your butt is NOT a dyno
Concensus is NOT science

Theres no answer to that question, to be more specific, you have to find that answer yourself.

Start with 87 for a few tanks and see how it goes.

No biggy

but Im a lazy ass so I just stuck 93 in it all the time.l

Use premium

I tried using 87 octane, after the third fill up I encountered detonation at > 6K rpms.
I gingerly drove to an auto-parts store and purchased octane boost. After that experience, 90 is the lowest I'll go. YMMV, but definitely pick up some octane boost if you are going to try it, this way you'll be prepared.

Cheers,

Alex

As always, lots of bad "science" in this thread.
Lots of misconceptions, hysteria and nonsense.


I have to agree with MM on this!!!!!

- Higher octane does NOT burn slower - it only has more resistance to premature detonation - which is more prevalent in high compression engines like the Renesis.

- Higher octane does NOT cause more deposits. For that matter, lower octane does not either.

Mazda recommends (but does not require) premium fuel for the 8 not only to resist detonation, but because most gas companies put more detergents in their premium gas - helping reduce carbon buildup.

For instance, Shell 87 has twice the detergents required to be certified as a "Top Tier Fuel" (a great fuel), but their 93 V-Power has 5 times the detergents. Many off-brand gas companies will have the federal minimum (about 25% of what Shell 87 has) and do not add any more cleaners to their premium fuel - so choose carefully.

Also, for those that premix, premix reduces octane and you should take this into account when making your octane choice. If you run premix with 87 octane, you are more likely running 85-86 octane, which I think is just too low. I think mid-grade 89 should be the minimum if you premix.

I suggest using FP60/FP3000 in every tank and then you don't need to worry about gas brand - and you have much more cleaning and lubrication than any pump gas will ever provide alone. I run an off-brand 93 premium (Wawa) with FP3000.

guys you are scaring me !!!! :o

in Cyprus we have 95 octane as the cheap solution.

We can use 95, 98 and 100 unlead petrol fuel!! i have been using 95 octane since i bought my 8 seven-eight months ago and i was thinking of 98 octanes.

So, what is the minimum and what is the maximum?????

it is different in the states... it is ron vs mon or something stupid like that.

your 95 = our 87. and mine works fine with 87.

beers :beer:

89 = 98
and 91 = 100 ? :P
lol...

omg.. for a moment i thought that there are fuels with these amount of octanes in fuel. :P

89 = 98
and 91 = 100 ? :P
lol...

omg.. for a moment i thought that there are fuels with these amount of octanes in fuel. :P

usa.

87 89 91.

if you dont live in cali. you get 93 or 94...

your 95 is our 87. your 98 is our 89. your 100 is our 91. same thing different systems of mesurment.

beers :beer:

omg my brain is fried.....

gees, read the manual.:eek:
http://www.rx8club.com/attachment.php?attachmentid=169099&stc=1&d=1299264713

Jp-7

regular and mid grade has always work better than premium in my 8. Also gets better MPG too

http://i9.photobucket.com/albums/a53/mushkid/I-dont-always-bump-old-threads-but-when-I-do-I-prefer-to-bump-4-month-old-ones.jpg

from the thousands of gas threads on this forum, it is know that using Regular gas makes the 8 perform Better.

Since it already got bumped by someone might as well chime in.

I know in my s2 it says premium required, so I go with premium. Right now premium is 3.70 a gallon, if I fill up 16 gallons thats almost $60. If I fill up 16 gal of mid grade thats only $2 cheaper than the premium, and the low grade is only $4 cheaper per tank.

Just pay the extra $4.

Since it already got bumped by someone might as well chime in.

I know in my s2 it says premium required, so I go with premium. Right now premium is 3.70 a gallon, if I fill up 16 gallons thats almost $60. If I fill up 16 gal of mid grade thats only $2 cheaper than the premium, and the low grade is only $4 cheaper per tank.

Just pay the extra $4.

yep:Peace: