I once saw a listing for a regular event hosted at a well-equipped shop with a dyno room. Participants, all hobbyists, would bring their hand-built engine in to run on the dyno. It was set up as a contest, with various classes, along the lines of SCCA's competition categories.

It just astounded me that such a thing would be a hobby, even though it's very close to something a lot of people indulge in by building up their race or road cars. But just build an engine from scratch and take to a contest by running it in a dyno room?

That sounds like so much fun that I would like to try it myself one day.