On Mon, 25 Oct 2010 18:48:23 -0500, Rick Morel
wrote:

Not water cooled, but a real world example. About 20 years ago I built
and flew a gyrocopter. It used a WW II era 90HP, 4 cylinder engine.
The manufacgturer's recommended mix was 25 parts 130 Octane leaded
aviation gas to 1 part 40 wt. aviation (mineral) oil.

Interesting! Do you happen to know Ken Brock? He was one of the
gyrocopter pioneers and flew one across country for the publicity.
He and I appeared together on a television show called "To Tell The
Truth" back in the early 70s. I was one of his "imposters" and Ken
of course was the real thing.