the manual recommends usage of 93 octane but in cali, i can only get 91 octane (unless i mix 100 and 91...but according to my calculations, each fill up would cost around $40 for full 93 vs around $20 for full 91)...so which makes me wonder, i know that using lower octane causes pings and other things in the engine but would consistant usage of 91 octane in any way harm the car/engine? like shortening the life span or anything like that...

 

No because they recomend the highest use of octane available...but the car was designed with Cali Regulations in mind...otherwise it would not be available for sale in the US. I personally wouldn't beat the living crap out of it though unless you are using slightly higher octane.

Just my 2c

 

I think the ECU will compensate by pulling timing so the only effect will be less power... Now if you manually manipulate boost and/or timing you may be in for trouble...