Algodoo

I suggest making the circles be delete a fraction later, and maybe making the circles half of that fraction larger (so longer strokes, more power in the same time, little more speed)

I just downloaded your "hit and miss spawn engine" then i checked this and you commented! haha, yeah i see what you mean there, i've still got a lot more tuning to do , i can't work out why it keeps spawn 5 circles at the time!, makes it too lagy for some people ;(

some things that'll always work:
use circles instead of boxes (as piston, fixate it, it'll be stronger)
use circles for spawners incase of boxes (single-collision point incase of 2 corners
use only one piston per cylinder
long power strokes
large spawned circles
use density incase of the number 15, when you enter the density of the spawned circle.

Well ballanced needs a heavy flywheel to smooth it out.
Nice looks on the pistons

Thanks bronie and gent