Algodoo

This collision engine is designed in such a way that it runs at a constant speed, whether it be at full throttle or idle.

Engine speed:

Idle - 16.15
Ful Throttle - 52.36

Throttle is controlled with the up/down arrow keys, and slowly goes back to idle once you rev it up and let go of the up arrow key.

It doesn't run perfectly smooth and consistent at idle, but it's pretty darn close.

Soon to be integrated into a single wheel car, so watch out for that. (if, you know, you like single wheel cars)