flyboi1121

i live in NJ and the sunoco's here have ultra-94 octane and thats the only one i'll feed my baby with.. it's only 1 more octane... but costs like 9 cents more than 93 octane... but it's worth it cuz i feel better =P

ddub

Since when?

Unless you are running non-stock timing or other modifications, running higher octane will not yield more performance, it will only hinder it. Until you do ignition and timing modifications or some kind of forced induction, it is best to stick with what is advised by Mazda.

I know for non-turbo earlier model rx7's you wanted to run the lowest possible octane of gas you could get.

Also remember, higher octane will cause more carbon buildup which is not a rotary's friend. Only run higher than suggested octane if you need to.


EDIT:
Since I haven't had a chance to actually look in my manual yet because I haven't even taken delivery of my rx8, what IS the recommended octane for the rx8?

rx8cited

Quoted from the owner's manual:

"Your Mazda will perform best with fuel listed in the table."
Table contains:
"Premium unleaded fuel | 91 [ (R+M)/2 method] or above (96 RON or above). "

Then under table:
"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've opted for the slightly reduced performance.

scottmhr1

Need to figure the math, if I use one tank a week, $0.20 difference in 87 vs 91, hmm, $3.00/week. Think for the performance will stick with higher grade. Hell cut out one of those starbucks coffees a week

Fanman

Mazda advises 91 Octane for optimum performance. Today's high compression engines have adverse effects from low octane fuel (vs. previous generation engines). The ECU will retard (turn down) timing & remove power. Many people who have run 87 octane whether because the quality of the fuel, or the terrain they are driving on have gotten detonation. 87 is about the lowest range where the engine can still compensate by reducing timing. Any batch of bad 87 (not really 87, might be slightly below 87) and you may run into problems. Unless you are talking race gas (100 octane+) it will not really hinder performance & it won't give much increase in performance either. The car is set to run on 91 octane, if you use 92 or 94 octane it can only advance timing so much then it is functioning at the factories "optimal" level (where Mazda feels it is safe to set advance). If you get a Canzoomer unit where can can advance the timing, you may be able to advance the timing beyond "factory specs and get more hp. I have seen some people/companies run a 91 octane "street" level, and a 100 octane "race" program on their ECU's.

jenkins-crew

So the owner's manual is wrong?

ddub

Your comment was only higher octane = better performance. This is definitely not always true. I dare you to run 91 octane in your car, dyno it, empty the gas tank, run 110 octane and redyno. See what happens, you'll get lower numbers.

Now if the rx8 was meant for 91 octane, then use 91. But don't expect that if you fill up with like 110 or 115 at the dragstrip to suddenly drop your times a ton.

jenkins-crew

Sorry I don't want my car knockin, that can't help the engine.

ddub

Did you even read my full post? I said

So if suggested is 91, 93, whatever, run it and be happy. But you will not yield more power from like 110 or 115, etc, at the drag strip on a stock car.

You were saying higher = more performance, that is wrong past what Mazda suggests. Why would higher octane just automatically make your cars performance increase when completely stock?

Now if you consider performance as fuel economy or engine wear, once again higher isn't better past what mazda suggests on a completely stock car. Higher octane, when not needed, will just cause more carbon buildup and worse fuel economy.