Bill Daniels

The cooling systems on motorcycle engines do not have sufficient coolant
flow to keep the head from over heating under prolonged running at 3/4
to full output. The water craft and snowmobile engines may have better
flow but these also have access to lower temp coolant.

Honda makes a personal water craft that has a hot little 4 banger engine
that I thought might do the job. It would take some testing to see what
it's sustained power level would be.

Car engines now are designed for full throttle continuous operation
because that's how the Germans run them. Actually another application
that does that, is the common school bus. Underpowered, they are run
flat out for a long time sometimes. Most now use diesels that are way
too heavy to fly, but when they ran Chevies, they ran a regular old
four bolt forged crank SBC.