Do you use premium?

[rrutter81]

I believe that premium has a lower flash point and is able to burn faster than 87, if i remember correctly? My z has a 10.5:1 cr and i know if i run 87 it will knock, ive heard plenty of stories. You can run 87 or 93 if you have your car tuned for it, but you will make less hp i know the differance in a cobalt ss vary from 87-93 its like 15-20 whp differance. I know if your cars suppose to run premium the factory probly sets the timing tables as they were using premium and they have the knock tables put in at what a lesser premium would do and retard it to that. The knock sensor will probly go ape sh!t when you add 87 and dip below the factory tune and start trying to retard itself so much its starts sputtering, etc. 93 is a more refined fuel and will burn cleaner and get better gas mileage for a fact, but this is a high comp motor im talking about. You will probly have no prob running 87 as long as you keep the rpms low. As for low comp and 87 it probly wouldnt matter a whole lot until you started winding it out but then you would probly sacrafice some power.

most intelligent post here.

however speaking from experience, I run BKR7E plugs and still got 4 degrees of KR on 93+octane booster. Im thinking they had a 97 Octane tune. It still drops to the lower octane table just incase.

Higher MAP will reduce the timing by default via the table so compression does have a little bit to do with it. However I would look at the problem, not the bandaid.

87 is more volatile, it will burn faster, which can cause preignition... 93 Burns slower, and so forth...

this is kind of right but also wrong. 93 octane can be compressed more before detonation. 87 is easier to cause detonation. If we were to take extremes like diesel it might become clearer?

I think a better way would be to say "which has a greater resistance" to detonation rather than saying something is more volatile under 0 psi.

What are you talking about?

it means that the timing map that is advanced 35+ (at least for me) degrees under normal driving was under the same octane rating as under WOT.