Small fun, big power: Pocket Bike with a V-type 8 cylinder Water-Cooled Engine.

Via: sticky note engineering

"This mini chopper using a scale engine by by Conley Precision engines is powered by a completely hand built, liquid cooled V8 engine, displacing 50cc. That's a model-airplane sized 6.25cc per cylinder! The engine is arranged like a small-block Chevy, with single cam OHV, including pushrods and rockers, driving 2 valves per cylinder."