On Mon, 07 Jun 2004 07:28:56 -0700, James Gemmill
gemmilljim@hotmail,com wrote:
According to my local service men I should be able to turn about 4600
RPMs with my 5.0 liter mercruiser. I am only turning 4200 at full
throttle, on plane and empty except for drive and one passenger. My
service guys say I can burn the valves at this rate.
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4200 is generally regarded as being at the low end of "acceptable".

Burning valves shouldn't be an issue if you keep your cruising RPMs
below 3400 and you're running at least 89 octane gas.

If you are still concerned, switch to a prop with slightly less pitch.