Algodoo

Well I can't really call it a rocket engine, And I didn't know what else to call it.

It is able to accelerate very quickly and can reach insane speeds, The demo scene has it on a simple vehicle. I spent a good portion of the night perfecting it, And I've got it running pretty damn good.

The engine motor is at 200 rpm and does glitch every so often but usually runs perfectly at 150rpm, The faster the motor the more acceleration the engine will put out. In the green laser's onLaserHit script you can change e.geom.density = 10000 to change the power of the engine, this can be as high as you want but it will weigh down the engine a lot and the main wheel will need to be made more dense to turn.

Also you may be able to tweek the springs to provide some better stability with the engine over 200rpm