RPM issues

dbond

Hello, I have a 1996 rinker captiva 232, 454 7.4 l.. Bravo 3 ourtdrive. I'm running 28 pitch props. wot, im at 4000 rpm's, at 49 mph. any ideas to better mph, and up my rpm's.. Thanks

Black_Diamond

What is the wot rpm number for your engine? With that you can change prop pitch to move the actual rpm +/- Generally every 2" of pitch moves the engine 400 rpm. So moving from a 28" P to a 26"P would give you 4,400 rpm.

dbond

Would that decrease my mph?? 4400-4800 is recommended..

Black_Diamond

It sounds like you are 2-4 " over propped. Too much pitch and you load up the engine hard. Too little you over rev. Your engine will be happier and performance will be better with the right props. Hard to say if you would lose any mph as you would be spinning faster.

dbond

Thanks for the info Black Diamond

KYSEAN

A 25 P would get you closer to your optimum rpm range with a little breathing room. 

Black_Diamond

I think the BIII only comes in even number pitch.

212rowboat

not necessarily.... getting to the powerband of the engine, dictated by cam, is the most important thing- that will dictate a window of pitch/diameter/design that suites the hull and engine...

you can do things like select a rake that provides bow lift... a cup that compliments that... a progressive enough blade that bites you in out of the hole but shifts down the face of the blade providing more forward movement per revolution.... props are a witchcraft..

the BIII are gonna make the selection an issue... they are too expensive to buy-to-try... maybe you can locate a prop shop with the blue props?  or maybe even one that allows you to pay a few bucks up front to test spin them...

dbond said:

Would that decrease my mph?? 4400-4800 is recommended..

Black_Diamond

I stand corrected on the pitch, you can get 1" increments. Your selection for a B-III is very, very limited and they are expensive. You might look at the XR props:

http://www.mercuryracing.com/propellers/bravothreexr.php

KYSEAN

Getting the correct prop will make the engine work the way it is supposed to. Don't worry so much about top end. Your engine is much more important. When you get the the correct RPM's at WOT. All the rest should fall into place.

dbond

sounds great..i'll try the 26 pitch and go from there, thanks guys