Algodoo

I was musing this afternoon on a kind of engine that could take an aggressive explosion, and slowly release the energy; something brutishly crude but not as mechanically rough as my stamp engines.
Came up with this /daft/ thing that has springs for connecting rods, and compresses them hard against heavy cranks.

Ignition on Q. It'll start from any position.

It'll run on low simulation rates. Clocked it at 91Nm@0RPM & 2HP@310RPM on only 80Hz, and up to 129Nm@200RPM & 4HP@460RPM.
More power can be seen by inceasing the strength of the connecting springs, but doing so will stop it running on its own / without the dyno dictating the revs.