I know a geek with too much time on his hands when I see one. I had to post this:
Miniature V8 engine.
And a video of it running.
This guy has built a supercharged V8 engine just a little bigger than a hand drill. It weighs 25 lbs, and spins 12,000 RPM. He made every part himself from plain metal stock. The hours involved must have been phenomenal.