007joe

iTrader: (1)

hey guys i'm finally getting comfortable enough to run my boat in the upper end more often. i noticed now that i'm only getting 4400-4500 rpm out of the boat. it is a 375hp 496, its supposed to be good for 4800 i've. i'm running a 28"p 4 blade bravo, i was under the impression it was a 26"p. if i switched to a 26"p would this affect it the way i think? (extra 400 rpm and maybe a couple mph) also how would it affect midrange performance?
thanks in advance

Velocity Vector

iTrader: (4)

Each pitch in smaller size will increase rpm by 200 so a 26 should do the trick to get you up to 4800. You'll just have to try it and see how close you get then you can lab it to fine tune the prop. I ran a 28 P in my 502 750 hp in a 28 donzi and ran 79 mph 5000 RPM. I will have to do the same thing on mine but I'm starting at 34 Pitch 4 blade Bravo one.

Pat McPherson

Yes, do try a 26p and compare to the 28p.
A labbed 28p will likely be the fastest but you may like the overall performance of the stock 26p better.

Velocity Vector

iTrader: (4)

A 26 P is actually a 25P 4800 RPM 14% slip shows 65 MPH 12% slip is showing 67 MPH

Your 28P is actually a 27P so @ 4400 RPM and 12% slip you should be going 66 MPH now and 68 MPH @ 4500 RPM

I would call a blade co and get the 28 labbed instead of buying the 26.

007joe

iTrader: (1)

another member may lend me a 26p (thanks in advance bill!)....... my 28 is supposed to be lab finished (by merc. i guess).... i've gotten 68.1 on the gps with my current setup and the tach was at 4400.... i think i'm going to try the 26 and see how it changes performance....

thanks vec.
by the way how do you calculate this stuff?

Velocity Vector

iTrader: (4)

Here are the formulas and the link is to a plug and play prop slip calculator
http://www.go-fast.com/Prop_Slip_Calculator.htm

If I can turn my 34P act a 33P @ 5800 and 12% slip I'm looking @ 106 MPH.

BBILL1174

Joe are you trimming it enough? The 28 labbed should be right I have to spin mine to 5600 rpm or I would be using a 28p

007joe

iTrader: (1)

bill, nice meeting you today!
thanks again for the loaner

BBILL1174

Joe Anytime I hope it works for you! Hopefully we'll be out Sunday it looks like great weather.