91 vs 94 Octane

[nocwage]

I'm wondering if there is any real evidence of a difference between running 94 and 91 octane in the FR-S. I've faithfully filled up my FR-S with PetroCan/Sunoco 94 since new so I have the wonderful idle chirp. I'm debating switching to Esso 91 in the hopes of eliminating the chirp and it simply being a much more convenient place to fill up.

Has anyone actually looked at any power difference or if timing will be retarded by going to 91?


Note, Canadian here, so not california 91.

[alanhung85]

Just go with Shell 91 0% Ethanol. No chirp.

[s2d4]

Is there ethanol in the 94 fuel?
If so I would still run that over the chirps.

[Decay107]

Go 94, 91 is pisswater.
These high compression engines need every bit of octane they can get if you are doing any kind of aggressive driving. The chirp will not hurt your engine at all, knock will.

[Reaper]

Run what's convenient. I would run the 94 in the summer if its hot there. It will resist knock a little better. Youll make more power with 91 though.

[Decay107]

Originally Posted by Reaper

Run what's convenient. I would run the 94 in the summer if its hot there. It will resist knock a little better. Youll make more power with 91 though.

Why would you make more power with lower octane? That should make the engine pull timing and reduce power.

[Reaper]

It shouldnt pull timing on 91 unless its very hot. The car was built for 91 since 93 is not available everywhere.

[Decay107]

Car was built for 93 it was built to "tolerate" 91

From the manual
"...The engine is designed to operate at maximum performance using
unleaded gasoline with an octane rating of 93 AKI (98 RON) or
higher. If 93 AKI (98 RON) fuel is not readily available in your area,
unleaded gasoline with an octane rating of 91 AKI (95 RON) may be
used with no detriment to engine durability or driveability. However,
you may notice a slight decrease in maximum engine performance
and you may hear some knocking (pinking) of an engine while using
91 AKI (95 RON) fuel. Use of 91 AKI (95 RON) fuel will not affect your
warranty coverage...."

[Reaper]

Car was designed for 91. Just like every other high compression car that recommends 93. You cant design a car to run on a fuel that only exists in a few places. They recommend 93 for a larger margin or error when considering hot climates, wear and tear, altitude etc.

[Decay107]

OK but still, regardless what fuel it was "designed for" (which we will never know since neither one of us was present during the engine's design phase) there is NO reason the car would make more power on 91 vs 93. Quite the opposite really as the ECU starts to pull timing (thus reducing power) even with 92 octane in my experience.

[Reaper]

Do you have a log?

[s2d4]

Originally Posted by Reaper

Car was designed for 91. Just like every other high compression car that recommends 93. You cant design a car to run on a fuel that only exists in a few places. They recommend 93 for a larger margin or error when considering hot climates, wear and tear, altitude etc.

what fuel do they run in japan?

[Decay107]

I'll see if I can dig up one of my old logs from the stock tune. Right now I only have tuned logs on this computer.

[jason.h]

Originally Posted by s2d4

what fuel do they run in japan?

98 ron which is 93-94 aki