Question about auto gas STC

Dave Stadt wrote:
: Actually it is like shutting off your car. Not a big deal by any means.

Actually, it's not *quite* like that. A car engine:
- Isn't timed to run at "really" low speeds.
- Doesn't have as much inertia as the propeller.
- Doesn't have as much idle load as a propeller at 500 rpm.
- Isn't air-cooled.

I have observed extremely low-speed dieseling on both high-compression and
low-compression aircraft engines when shut down with the mags after flight on cargas.
It initially worried me, but when I thought about it more, the following two things
were important:

- VERY low speeds (50-100 rpm), so 25x more time for the fuel to preignite than at
takeoff conditions (2500 rpm).
- VERY high manifold pressure due to idle throttle at very low RPM... almost full MP.

Both of those equate to serious "lugging" conditions on a hot cylinder head.

YMMV
-Cory



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