Algodoo

My first successfull spring engine, with variable throttle to boot! Nearly all of the instructions are in the scene, just be sure to read them before you unpause the simulation.

The reason for waiting to unpause it, is there's a box that says to have the simulation at 300 or 500Hz, or the engine won't work (it may even explode).

The throttle goes from 100% to 1%, and the engine may die if you put it at 1%. If you make the engine do any actual work, then it'll surely die at 1%.

The engine will run at around 500rpm as its idle speed, and full throttle it runs at around 1800, if the sim frequency is right.
If the engine doesn't work at all, or works poorly, tap the Tilde key (~) or F11 and type in "Sim.Frequency = 500" without the quotes.

If your computer lags at that frequency, try to change the frequency to 300, but not anywhere below that.