Algodoo

If you're actually familiar with Phun/Algodoo you may have made negative spring engine in the past - they're extremely simple to make, yet hard to master.
Here's exact opposite of negative damping engine. The engine works by pushing the spring at the right time to push the piston down.
When the piston is at the bottom, the rod will pull the piston from there, and the cycle repeats. Minimum speed: approx. 50-54 rad/s
Controls:
Engine: S - starter
Vehicle: C - toggle clutch
Note: once the engine stalls, it's pretty hard to restart by hand. That's why I'm using thrusters to crank the engine until it starts up.
Scene runs @ 240 Hz.