Time and time again claims are made that diesels make more power. This is NOT true of every engine. The original post is about going fast. Every engine diesel or glow makes peak power way up in the RPM band, not lumbering along at 7-8kRPM.
I always point out the MVVS 2.5cc. From the factory both are rated at similar peak power and RPM. They are rated at .7HP at 26-27kRPM. The diesel does just fine swinging a 9x4 at 12kRPM, but it's not making anything near .7HP. Tuning for speed is a complex matter and one might find that top speed is with a prop at 18 or 20kRPM, but you won't have a chance at going very fast at 12KRPM regardless of the prop.
ORIGINAL: Ralphbf
The reason people put larger props when moving up to diesel is the increase in power.
You should beable to increase the pitch instead of the length to better use the extra power.
Dare I say that most who run diesel want more power but not more speed
that is why they go with the longer prop.
I have mixed feelings on the tuned exhaust.
I don't believe you would get as much gain as with non-diesel engines,
because of the more effecent combustion.
But you start off with more anyway.
Just my 2 cents worth.