As stated in another thread, I once worked for Exxon, and you are pretty much dead on. I would never run lower than recommended octane in a forced induction engine or an engine with extremely high compression ratios regardless of pcm programming. My G Force showed runs virtually identical 0-60 performance using first, 3 tanks of premium, then 3 tanks of regular in nearly identical hot assed summer weather. I just left it in drive and went from a dead idle to help equalize the runs. I guess the spark advance with the premium is not enough to have a major effect on my truck's acceleration.

 

My car has always had a lot of power, chirping the tires in second. But since I have switched to 93 oct, Its got even more power. If I get out of it and then get back in it at around 25, I chirp them. I have also noticed already better MPG's as long as my foot stays out of it, and I am only on the first tank.

 

Ok, so what I don't understand is this... How come a 2.4 in an HHR says premium is recommended, but the same 2.4 in a G6 says 87 regular is all that it needs? Same engine, different car...

 

Same engine but different states of tuning between the G-6 and the HHR. The LE5 in the G-6 was good for 169hp and 175hp in the HHR, doesn't sound like a lot but apparently enough that Chevy recommends premium for the HHR.