What limits the size of the prop?
 

I'm running upwards of 640+ HP, actually 540 HP at 4000 RPM to 648 HP at 5300 RPM, yet I am only able to turn a 28P Bravo1 prop 4650 RPM.

It actually seems like as I push the throttle to the max, my HP drops off! Engine has less than 10 hours on it. I've taken it easy for break in, but want to run a little now!

Last year before the rebuild, I was able to spin a 29 at over 5000 RPM.

What limits the size of the prop I can turn, shouldn't it be the HP and torque? I should have enough of both to spin a 28P faster shouldn't I?

Just curious. . . and a little disappointed

What is your HP and TQ curves every 250 rpm or so?

I bet 4650 is right near your TQ peak!

4000 - 542 HP, 711 Ft-Lbs

4250 - 580 HP, 716 Ft-Lbs

4500 - 604 HP, 706 Ft-Lbs

4750 - 623 HP, 693 Ft-Lbs

5000 - 628 HP, 661 Ft-Lbs

Peak Torque is around 4650, but the HP is still going up.
With a 4500# boat, Deep V whats the recommended prop. Darin at Houston recommends a 26 Bravo 1 repitched to a 27, cupped and labbed. I agree at this point, but just like to get several opinions/ideas.

Thanks

What speed are you running at WOT with the 28"?

I would try a stock 26" and get the numbers and then talk to Darin.

Before I labbed or cupped a prop I would test the 1 and 2" shorter lowers. Maybe trying different lower units (shorter) might help more.

Shorter? I'm running a 17-1/4 X dimension already!

I am turning a 28 labbed Bravo 1 4850 in 90 degree heat and high humidity with a 575sci on my pantera 28.

Something is wrong.

I think labing that prob would get you to 5000, but maybe a labbed 27 would be even better, you would probobly turn 5200-5300

What could be wrong? Engine is strong, boat seems smooth and good. This is a stock prop no modifications.
Should still be getting the RPMs up. I'll try a 26P and see what happens.

High Tide - I ran the dyno. Did 15 - 20 pulls all the same.

What is the drive gear ratio?
Dennis Moore

Call Matt or Julie at Throttle-Up Props. These guys can get the most out of any prop, and they are the best people you will ever deal with.

Throttle-Up 727 531-2256