well, my buddy just got an rx8. im trying to help him out the best i can. does the low octane theory for na 13b's that i read about in the 2nd gen forums apply for the renesis 13b? (better gas mileage, cleaner burn, a little more power,) thanks -alex

 

Mazda reccomends 91+ for the rx8, but say you can use 87 with some decrease in power. How true that is who knows.,... maybe the rx8 runs crazy advance curves and retards them for 87,... its got a knock sensor im pretty sure..

 

Octane = stick to manufacturer's recommendation.

Visit the RX-8 forum

www.rx8club.com

and ask them.

 

Since buying my car new last November, I've kept track of fuel mileage. I've ran lots of super, plus and regular. I've noticed no different fuel mileage between any of them. I allways seem to get between 19.5 and 21mpg. Sometimes, I'll get 21 with regular, sometimes with super. Most has to due with driving style.

For power, the 8 does make more power on higher octane fuel than lower octane. A friend in Rotary Power NW and I did back to back dyno runs with our cars. I was running super and 5 gallons of 110 octane race gas in my 8. He was running plus I beleive. I made 11 or 12 more rwhp than he did. I also made peak power up against the rev limiter. Infact it would'nt have stepped in, it would have kept climbing! His car made peak power between 8-8.5k I think. Bolth cars had around 2.5k miles on them. Bolth 6 spds....but I do have the rear wing....maybe thats where I picked up the couple extra hp?

If your friend wants the best fuel mileage as possiable, I suggest keeping the engine below 3,750rpms. Its pretty hard though...and most people did'nt buy the car for fuel economy. The 8 is a awesome car to drive.

CJ

 

Higher octane fuels often have more aromatics, which helps them burn quickly. It depends on what brand fuel you use and what area of the nation you are in. (EPA mandated different fuel blends for different areas of the country depending on many factors)

Some people run race fuel and *crazy* timing (like 30-35degBTDC) on N/As...

I used to be a low octane believer but the more I learn the more I might change my mind!

 

yeah keeping it under 3700 is HARD! its too much fun above that

 

Manufacturers always suggest higher octane for high compression engines. Since the renesis is higher compression, you need the premium gas.

 

higher compression = needs better gas

 

perhaps. however the renesis has only .3 higher comp than an s5 n/a (9.7 vs. 10.0). s5 n/a's, including my own, are known to run perfectly fine, if not better, on lowest octain gas.
the rx8 has an vastly more advanced EMS than the FC's. whereas fc's go pig rich and have relatively conservative spark advance, the rx8 is probobly much more agressive with AFR's and timing in order to make 50% more power out of the same 1.3 liters.

the 91 octain probobly serves somewhat as the "safety net" on the rx8 where the FC's "safety net" comes from the conservative programing.


pp13bnos, thats very interesting that you makde ignificantly more power on the race gas but could still drive safely and effecintly on 87!!. do you have any more knowledge from owning one yourself on how the ecu functions and what might alow this?

 

I don't have a clue. Seems like no one has realy cracked the ecu yet. There are a couple piggy back ecu's out on the market that add 30+ hp....but I'm waiting until (hopefully.) the P-FC comes out for the 8. CJ

 

As a post ***** in training in the RX-8 Club, there have been several threads regarding using lower than premium fuel. Apparently, some people have been using 89 octane without any problems. Unfortunately, I don't know of the long term affects of constantly using 89 octane. Personally, I use 93 octane (Texas ) just to be on the safe side; like you guys stated, a higher compression may necessitate the use of a higher octane rating.