i just switched to 89 from 91 (shell) and noticed a huge increase in mpg. the power difference wasn't measured so it might be a placebo but who cares. it just feels better. i did a full tank of 89 and took the same trip from sacramento to reno. same driving conditions, pretty hard on it in fact. topped out at 111 on a particular stretch of deserted highway. previous tank at 91 got me 16.75 mpg, the 89 tank got me 21.0. i've seen reports on the difference some of us have been getting and was a bit skeptical. i'll do a couple more tanks to see if it was a fluke. anyone else see similar results? and more importantly, will the 89 hurt the car at all?

 

The problem with running too low of an ocatne rating is predetonation, which from what I understand is pretty bad for rotary motors. Running too high of an octane can indeed hurt fuel efficiency, basically because it's a bit harder to ignite and burns more slowly. I run 89, and I still get really crappy milage. I don't think 89 is going to cause problems personally, but I don't have anything to back that up.

As temperatures rise you may want to increase the octane, to help prevent predetonation. Personally if it's giong to be around 95+ I run 93 octane to be safe.

 

I thought of trying 89 also, so I mixed it in with 1/2 of 93 and 1/2 of 89 and the car was ok. But after it ran out, I put 89 completely and 5 mins before hitting the highway....she didn't like it and CEL turned on. I guess, she doesn't like cheap stuff :p Now I'm back to 93 and she's happy (women = my car that is)

Al

 

im running 87 right now. because thats all you can get around here right now.

actually feels pretty damn good, im keeping it off load as much as possible, but no signs of pinging yet

 

i always run 89... never had any pinging issues and i seem to be a few more mpg out of it compared to 93 octane

 

10k+ miles on Shell 87 octane and no pinging or no new engine required yet .

rx8cited

 

I had 10mpg city and 14mpg highway on 93 octane on my new car with 3000 miles. I switched to 87 octane and my mileage jumped to 14-16 city and 21 highway.

The RX8 is strange in this way.

Steve

 

back when i had an rx7, i was told to use 87 octane as it burned the fastest, which is desireable for a rotary. (octane as a measure of resistance to ignition).

james

 

I tested all grade (87, 89 and 91) but could not see a difference. Never pinging, but some brands make the car feel better than others, for the same octane. It could be that my car is still too new (3400 miles) to distinguish those yet, but for now I settled with 89 but from good companies (Shell, BP, Texaco). I get about 18-19 mpg, mostly highway, not many redlines ;o) It's an auto anyway.

 

I ran 87 in the FC RX7 and I run 89 in the RX8. I get 20+MPG consistently even if I sometimes flog it as I enter the highway. It is N/A, so 89 is plenty high enough octane. Don't waste your money on 91 or higher, not worth it unless you have a turbo or SC.

N/A rotary engines like lower octane fuel.

Kurt G.

 

I've used 91 for 20k miles

87 may hurt the car , 91 won't hurt the car
so why use 87

 

richie, you would get 16.75 mpg on the highway? Man, I thought I had bad mileage but 16.75 on the highway is pretty lousy. Glad to hear the change in fuel grade has helped.

I tried two tanks with 87 with no change/no improvement. Otherwise, it's been 91 in my car. I may give 89 a try and see what happens.

Keep us posted if you have notice any changes.

 

I've had my car almost a year now and closing in on 9K miles. I would hit 1/4 tank with 170 miles with 91...just filled up with 89 and I'm currently at 210 just barely below 1/4 tank. I estimate about 19 mpg (city type driving). Not sure why people are getting such horrible gas mileage. I also shift from 1 -3 and 3 -5 occasionally. (Easier on gas and tranny)

 

Red8, holy crap! Your car is almost one year old and you ONLY have 9k miles on it?!

 

Yeah, moved to NJ in January from Georgia...car stayed at my parents house in SC for 4 months! Wasn't about to let it see the snow! Plus I drive a "beater" truck to work on bad weather days. Oh, and one GOLDEN rule! This car doesn't go to Wal-Mart type shopping centers!

Damn car is pampered!!

 

Nothing wrong with that bro... :D