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What is the lowest octane an RX8 can safely use?

Old 03-14-2006, 10:54 AM
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What is the lowest octane an RX8 can safely use?

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
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Old 03-14-2006, 11:05 AM
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Before you are set on fire by the search-****'s here, I'll say check your user manual. I cannot remember for certain, but I think 89 is too low.
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Old 03-14-2006, 11:08 AM
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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.
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Old 03-14-2006, 11:12 AM
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According to the manual, 87 is acceptable. Mine runs fine on 87. Some others don't.
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Old 03-14-2006, 11:24 AM
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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.
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Old 03-14-2006, 11:29 AM
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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.
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Old 03-14-2006, 11:49 AM
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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.
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Old 03-14-2006, 11:58 AM
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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.
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Old 03-14-2006, 12:01 PM
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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
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Old 03-14-2006, 12:02 PM
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Yeah, I run shell "v-power" 87 pretty much exclusively.
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Old 03-14-2006, 12:11 PM
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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. ^^
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Old 03-14-2006, 12:13 PM
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Yes, it has timing, silly. You think the spark plugs just shoot off randomly, lol
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Old 03-14-2006, 12:14 PM
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of course Renesis have timing, wtf
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Old 03-14-2006, 12:15 PM
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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!

Can anyone help to define ***good*** gas? I always shop price, am I being stupid?
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Old 03-14-2006, 12:18 PM
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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??
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Old 03-14-2006, 12:56 PM
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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...
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Old 03-14-2006, 01:44 PM
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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.

Last edited by Raevik; 03-14-2006 at 01:49 PM.
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Old 03-14-2006, 01:51 PM
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Unless someone can quantify a real risk, I'll take my $2, better mileages, and smoother running that I get with 87 octane.
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Old 03-14-2006, 03:00 PM
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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?
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Old 03-14-2006, 03:09 PM
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Originally Posted by Raevik
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.
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Old 03-14-2006, 03:11 PM
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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.
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Old 03-14-2006, 03:14 PM
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Originally Posted by Red Devil
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.....
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Old 03-14-2006, 03:36 PM
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^^^
won't argue with that
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Old 03-14-2006, 04:14 PM
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Originally Posted by Raevik
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).
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Old 03-14-2006, 05:57 PM
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Just use 98 octane like me, then you dont need to worry at all 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!!
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