Octane

[nemesis]

hp doesn't necessarily cause less hp, less torque. Every engine is designed for a certain octane, like 5.0 mustangs came with 9to1 comp, the best gas mileage and hp with 87 octane. Now same engine with 10to1 comp would make more power and better gas mileage with 93 octane. Modern cars with aluminum blocks and heads can have 10.5-11to1 comp and still run pump gas (93 octane). If you put higher octane in a 9to1 comp engine without adjusting timing all it will do is make carbon, you will not gain any more power/mpg. My 00 3.8 stang gets the best mileage with 87 octane, it's just my daily driver. My 89 2.3 turbo stang ( 8to1 comp), will run on 87 ok with 10psi ( around 140hp), with 93 octane it makes over 230hp with 18psi, race gas 110 octane I get crazy with timing and run 25-28psi, it makes close to 290hp, so octane does make a difference, you just have to use it right.

[MadisonMPG]

2 words.

Advanced timing.

[Johnny Mullet]

I have to run high octane. If my car was stock, I could run regular.