Algodoo

my face when I saw that thing

Nice design.

It's good
try making the spring lenght to change between 0 and 9 m, but not the constant.
And get rid of damping

That's how it was. IT was way too unstable, Very jerky motions between strokes and throttle control didn't really work with constant instead of length for throttle. if I used constant to change the throttle, it would be far too weak at low RPM. The way I have it now, the engine maintains the same amount of torque at any speed almost. and as far damping goes, it's just to keep the springs from being unstable. the power is pretty much the same damped or not. I haven't tested it a bunch, but it seems fine either way.

Yes, you're right. It only gains 1 Nm more, and 5-10 rad/s, it isn't much.
anyways, I'm waiting for the vehicle ;D