DF300's Maximum RPM Questions

[rocksalt66]

Maximum engine RPM: I have twin DF300’s on a 1990, Wellcraft 2600 Coastal with a 30” full hull extension bracket. My normal load with full fuel (200 gallons) and gear is 10,000-11,000 lbs, My maximum engine rpm is about 5700-5750 at 53.3 mph, and I run the 3x16x21.5 Suzuki prop. Does this seem reasonable at this load? The Suzuki web site shows tests with similar size boats using the same prop and getting higher RPM. Even thou they don’t seem to be working hard, I am I damaging my motors operating at the bottom of the recommended 5700-6300 rpm range. Any recommendation on other props, 3x16x20, or the four blades 4x15x20, or other brand props?
Thanks

[boats.net]

Keeping rpm's on high side of rpm range generally gives better fuel economy and is better for the engine.

[jaysonbarn]

Lower RPMs cause permanent engine damage. Its my experience. Go for higher RPMs will definitely improve efficiency and performance...

[bootleg]

try a set of 19p props and get full rpm at your highest trim level????