So I have a base 05 RSX, am I looking at ANY performance increase with 91 Octane (I live in CALI) or is it just a waste of money?

 

save your money

 

I second

 

headers, intake, exhaust wont make a difference in octane usage?

 

na. not unless its tuned for whatever octane gas you are going to run.

 

Agreed. Additional you would ideally have the compression ratio necessary of utilizing higher octane fuel. I have no idea what the base engine CR is,though.

 

i think they are 9.6:1 static compression. honestly if the motor is old or had a bit of carbon buildup in the cylinders where it may be more prone to knocking you could see a benefit from 91 octane. if it knocks less than the knock sensor will pull less timing which equals more power.