I understand your reluncancy for canned effects, the merit for calculation of everything is shown with the difference between LFS's physics and everything else i've had the pleasure of trying.
My point was that for a few extra lines of code, and no issues with the hot laps etc, Any impact with a force great enough to bend the engine compartment to half its size, and almost past the front wheels, (front engined cars only, i should've mentioned that.), would definately stop the engine, so it's safe to code in at such a high threshold without worrying it'll happen without due cause (as often happens with canned effects).
I also feel this could help cut down on wreckers, who can drive around the track with a car bent over double, and still propel themselves into the path of on coming cars.