Does anyone have a good formula that combines effective compression with charge temperature to find an octane requirement?

I took my 2200 out last night intercooled for the first time, and IATs were around 71F under boost with an ambient temp of 59F. This was after burning about 1/3 of a tank of fuel in order to train the EIC, which consisted of 2 hours of 5-6 PSI pulls throughout the rev range. The turbo was glowing red hot after I pulled over, but IATs were still in the low 70's. Before the intercooler, IATs were towards 200F and the engine would knock hard above 4 PSI. Last night with the IC, there was no sign of knock at all.

With IATs under 80F on a 2200, how much boost would you guys shoot for? How high above ambient are your IATs?


2002 Cavalier 2200 5spd

For what it's worth, I'm up to 10 psi now with no sign of detonation. The EIC holds the AFR right at 12.5:1 from 1750-6250 RPM, and from 0-10 PSI. Is there any reason to go richer than that if you're not pinging or does it just hurt power?


2002 Cavalier 2200 5spd

You should be fine. Keep an eye on it when air improves, such as colder weather. Usually, anything from 11.9 to 12.5 is good at this boost. You would start to lose power below 11.9.




Bill Hahn Jr.
Hahn RaceCraft

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