Re: 87 omc 305 WOT RPM range
Just curious on what the range for WOT on this engine is? And how do I know if I'm over revving it by trimming to far up?
Its a 305 punched out 30 over in a 87 chris craft 21ft cuddy with a 14.5x19 SS prop. And would changing to a 21 give me more top speed?
Howdy,
Your owners manual (or service manual) should indicate the correct WOT range for your engine. (usually around 4200-4800 RPM for many V-8's)
Trimming the drive in or out during high speed operation will usually produce the fastest speed. If you trim too far in the boat will "mush" and slow down(and possibly make a growling noise etc)
Trimming too far out will also slow you down, cause porpoising, and possibly prop cavitation.
You find the "sweet spot" experimentally at just about every different speed.....the trim position gage is useless for the most part.....
Omc, Mercruiser, and Volvo (and most outboard motor manufacturers) recommend prop selection that gives the top of the recommended RPM range at wide open throttle (WOT)
There's a VERY narrow range of (prop)RPM that is efficient. You cannot just keep "cranking" the pitch up and expect faster speed. At some point you'll be severely "lugging" the engine and possibly cause damage from detonation...
To know if you're properly "propped", you must know your RPM accurately.
That means a KNOWN tach.
Assuming your boat is not overloaded (either with people, stuff , waterlogged) or has STUFF growing on the bottom slowing it down, you need to know your speed accurately to make prop decisions too.....
If you're turning around 4800-5000 RPM at WOT, you're probably right where you need to be........A 21 might speed you up a little, but your hole-shot will suffer
Cheers,
Rick
