I only have access to 92 and 100 octane. Well, and crappy 93 that is 10% ethanol. Anyways, what is the ideal ratio of 92 and 100 I should use for daily driving?

 

http://www.collectracecars.com/octcalc.htm

Aim for 94 - 95 pump octane.

 

Basically, its just...The more the better. So there is really no point in even trying. You might as well stick with 92 and use pure 100 for race day.

Whats wrong with ethanol?

 

Last Friday while I was at the track, I put about 2/3 of a tank of 100 octane in with my existing 1/3 of a tank of 94 octane, which should have given me a blended octane around 98. Then Monday night, after the low fuel light came on, I filled up with 93.

It made a believer out of me. The stock ECU can and will take advantage of octane levels well above the 94 octane that I usually run. I know this because I don't feel any substantial difference when I switch between 94 and 93, but felt a very immediately noticeable difference switching from 98 to 93. Going back to 93, the car felt underpowered and hesitant, sort of like it does after a cold start (but not as dramatic).

I am not sure how much of this was due to the ECU retraining. Perhaps it had retrained to the 98 octane, then it detected knock with the 93 octane and dropped back to a "safe" ignition map. But if that's true, that means that the ECU will advance ignition enough to make the engine ping on 93 octane gasoline, which indicates to me that the ECU is more adaptive than I'd been led to believe, and that putting race gas in the car (compared to 94 octane) is probably money well spent if you need the performance.

 

jbrennen, I am in the process of conducting a similar ***-dyno test. Right now I'm blended at about 94.6 octane, but I will bump that up next time I fill up. I am doing it on a smaller scale from now on (1/2 tanks) to save a little R&D money.

The car definitely seems happier with the 94.6 octane I am running now. 'Course that's a rough estimate, I could be anywhere from 94-95 octane based on the amount of 93 that was already in the tank. The cold air we've had lately (~50-60 degrees) is really getting taken advantage of right now, such a difference from the weezing summer days of 80+ degrees.

 

Octane is valuable, believe it. Nevertheless, its a expensive and addicting drug. Your best bet is to make your car perform with what you have.