wheel is probably a 16x15 with a big cup

the newer MPI motors have the torque to turn a bigger wheel

older 260HP carb'd small blocks should be running a 16x14 with a cup

allways want a cupped prop - the cup acts as a little more pitch and it holds the water - less cavitating

With a nicely shaped 3b 16x16 and a 260 hp motor, you should cruise at 20 kts, and top out at 28 kts, depending on a whole lot of stuff.

But the unvarnished truth is that you're not going to touch 40 kts without at least 500 hp, (and probably not even then) simply because of your angle of thrust.

Too much wetted surface=too much drag. You'd have to fair your tunnel, then extend the shaft and rudder out of the transom to get the thrust angle within about 2-3 degrees of your keel line. Too much continual stern lift results in too much forward water displacement resulting in too much drag.

I knew a 23 inboard in North Palm Beach that was repowered in the 80's with a 375 hp small block, and she topped out at 31 kts, or 36 mph. That long-duration cam sounded great, and it nearly jumped out of the water from a stop, but the laws of physics still prevailed.

Thanks for the input.
I will likely stay with the PCM 353.
The torque from the watercraft motor will give me what I want for the cruise.
The wot remains to be seen at the end of it all!
I have been using the spec sheet for the calculations and the following link.

http://www.vicprop.com/planing_size.php

17x17 prop 454 inboard 23'
 

I had a 17x17 prop on a 23' cc with a 340hp 454. Ran great, awesome control at low speeds and insane hole shot. Clearance in the pocket isn't an issue, no turbulence at all.

Right now with an unknown hour 351w with probably 235hp I’m seeing a cruise of 24mph, a top speed of 32mph. This winter it’s getting pulled and rebuilt to add some serious horsepower to it, with this being said, I don’t see how with 130-160 more horsepower I won’t pick up speed, EVEN if I have to change the pitch and add a trolling valve.

Think Big.....
 

If I was to ever own a car engine boat it would have one of these.

Amen to that