Somethings Wrong
 

Speed is way off. 38' Cougar V 66 mph @ 4400 rpm with dynoed 623 hp @5600 rpm. Speedmaster 4's w/ 2 inch spacers turning 17 1/2 x 26 3 blade cleavers. 10-12 slip should be around 77-78 mph . Where do I begin??

Call Matt or Julie at throttle Up. they can run the numbers for you to see where to start.

We specialize in these K Long Hubs. If in your opinion, you are off 1200 rpm, there is a hp issue going on here. Even if these propellers have been repitched, it couldn't be done far enough to get you down to the point you are at. What I am suggesting is, the hp may not be where you think it is. The props you have make sense for the application

If your gear ratio is 1.5:1, the slip is at 12%. For this hull, you are doing great. 5150 would give you 77 at this slip % So actually you are off 700 rpm with these props to get to your target speed.

I would try some other propellers. Anything you can find to compare.

The dyno sheet shows 682 trq @ 4200 rpm, and 584 trq @ 5600 rpm. Seems to hit a wall @ wot and only getting 4400 rpm and 66 mph

Sounds like you've got too much prop. Is this a totally new set up or do you have a baseline from another power/prop package to compare???

From your numbers, it looks like you hit the wall when peak torque starts dropping off and you can't get over the hump into the peak rpm too make max HP.

I agree Griff. Drop down a little in pitch and I bet it gets you over the hump.

Julie

This is a new set up with existing props. Less pitch with the 3 blades, or any ideas on 4 blades? Btw in the process of installing better heads which should then dyno 725 hp.

I would wait till the new engine mods are complete and try the current props.
My feeling is you might end up needing 4 blades.

Your boat likes 3 blade props. This is evident with the current slip #'s. It isn't going to run too much cleaner.

Yes of course you need to go down in pitch if you want the R's to go up. If you can't turn these props any harder, the HP is down and the pitch must go down if you need to get to low to mid 5000's to save the motors.

Finish the engine work and work last on proping.