Daniel J. Stern wrote:
> On Sat, 14 May 2005, dyno wrote:
>
>
>>True. There's also the inlet temperature effect; temp up octane
>>requirment up.
>
>
> Oops, no. Ambient temperature goes up, octane requirement goes DOWN, and
> for the same reason that octane requirement decreases as altitude
> increases: With both increasing altitude and increasing ambient
> temperature, the intake air charge is less dense, therefore cylinder
> pressure is lower, therefore tendency to ping is less.

Wrong. The change in density goes with the change in absolute
temperature. But, the effect of inlet temperature is magnified during
compression. The compression effect dominates over the small change in
density.