Brad
Kushner sends:

http://www.popularmechanics.com/technology/a21324/engine-startup-liquidpiston-powers-a-go-kart-with-a-4-pound-engine/

Connecticut-based startup LiquidPiston announced today that they
have built a small, compact engine that is powerful enough to drive a go-kart.
Their X-mini engine weighs just 4 pounds and has three moving parts, and yet can
produce 3 horsepower, enough to replace the default 40-pound piston engine that
normally powers the go-kart.

LiquidPiston says that their X-mini is still in a testing phase, and they hope
to get the weight down to 3 pounds and the power up to 5 hp. (The 40-pound
piston engine produces about 6.5 hp.)