i used to run a 1.32 alpha behind a stock 330 that could turn that rpm with a 23. its a smaller boat but 350hp difference is a lot. sounds like its out of power to me. i would try props first. its way cheaper and easier too

Try you a 22 Bravo and see what that does, thats a big old girl for a Single , 1.50 would be a way better choice for Acceleration

Beings how we are pretty sure that the 1.5 is the way to go, or at least can be nothing but better, been working with a shop to change it over.

650hp in a 29 Scarab should be able to spin a 28" with a 1.5 ratio Bravo drive to 5000rpms +. 650hp out of 598 should be torque monster and pull hard all the way to 5000rpms. Post the dyno sheets if you can.
Changing to a 1.34 means he needs about 3" less pitch all things being equal. The SCX throws a wrench into the equation.

I'm basing this on the fact that I could spin a 26" Bravo on my 28 Pantera with 550hp to 5300rpms.
I also have 1.36 Bravo's on my 32 AT and spin 24 Bravo's to 5100rpms with 502mpi's.

First thing I'd do is check ignition timing. Next, I'd check for hook in the last 3' of the hull.

Did he run the boat ever before the rebuild???
I really don't think the 1.34 ratio is causing the problem

Griff, Yes timing has been checked. its set at 34 now. Yes he ran the boat before rebuild.He's only had the boat 2 yrs now. It has never ran since day 1. It was the same thing, just couldnt get over the 4200. A leakdown test showed motor needed some TLC, thus the tear down and rebuild this winter. Havent thought to check the hull. Thanks

The SCX is like taking 300 hp from the boat compared to a SC