Took boat out finally ran great except bad cavitation trying to get on plane. on plane very smooth handle good. 2000 firehawk cat (looks like a AO) 2600, 600HP 1.50 gear Has a 3 blade 27P think I need a 4 blade but have no idea of pitch

Usually when you go from a 3 blade to a 4 blade you go down one size in pitch. Need to know your RPM's at WOT to know what pitch you actually need.
By the way are you running cleavers?

Just bought the boat dont know a whole lot about it. Motor has 10hrs wot rpm about 5400 dont know speed forgot the dam gps not cleavers

Hoping too get close so I can get some test props and then fine tune from there

call b blades they will work with you on different pitch props to try. So you can find the right pitch..

I agree, probably a 26 or 28 Bravo, depending on what RPm he wants to turn the motor. We run a 26 AO, and it is tought to prop also, Ray would know for sure his pitch, but it I am sure it is somewhere in the area of a 28 Bravo.

I would start with a 28" Bravo 1. It seems like it should be about an 80mph boat or so.

I listed a 26 repitched to a 27 bravo one , labbed by bblades perfect blade $ 500.00 shipped

thanks for the advise on pitch i'll give the 28 pitch a trial run and see what happens

IMO if your having blowout problems with the 27P 3 blade then you need to go to a 25P 4 blade.