I have been using Petro 94 since I got my BRZ (end of August) and for the past month and a half I have been keeping track of my mileage.

Week 1: 10.41KM/L
Week 2: 9.24KM/L
Week 3: 9.33KM/L
Week 4: 9.39KM/L
Week 5: 9.35KM/L
Week 6: 9.49KM/L

Week 1 contained a lot more highway driving than I normally while the other weeks are all in city driving with very minimal highway driving (approximately 10KM/day).

Have you tried the same test with shell91?

No. I decided when I got the car to just go with what the manual says, and although it says 91 is fine, I am going to stick with 94 for now.

I need to clarify a few things, first petro stations that have 94 used to be be Sunoco, and any petro stations that were in competition with them i.e across the street were converted to husky stations. At least that's how it is in Ontario. Secondly it is useless to fill your tank with 94 octane with temps below freezing, the reason for this is that the air temp is so cold entering the engine pre ignition and detonation will be a non issue. But when summer comes that all changes and believe me your car will runner better with 94 on the hottest days. I can Certainly feel a difference in the butt dyno and also an audible difference! So I truly believe that it is possible for a gain of 5hp. Having said that the reason I stick to this is because I had shell 91 on a 35 degree day and it didn't feel or sound right, so I added a NOS octane booster=6 full points of octane-but bad for the catalytic converters, and wow what a difference!!! There is something definitely up with this car not liking 91 on hot days! Hope this helps.

It doesnt like 91 because the Compression ratio of the engine is skyhigh. It is tuned to use 93 octane as the manual states so anything less and it is not going to make the same timing.

This is even more apparent in summertime when the charge entering the engine is less dense.

hmm... i'm thinking maybe i should use shell91 in the winter and Petro94 in the summer, but i heard Petro94 is not so good on MPG that means in the summer i'm gonna spend even more money on gas :(

[QUOTE=fenton;773842]It doesnt like 91 because the Compression ratio of the engine is skyhigh. It is tuned to use 93 octane as the manual states so anything less and it is not going to make the same timing.

This is even more apparent in summertime when the charge entering the engine is less dense.[/]

Yup, I knew this already, and completely agree. Thanks.