Ok heres whats going on. I have a 1988 32' Hydra Tech Cat. Repowered from 468's w/ about 550hp, Bravo 1's, 1.5 w/ 30P 4 blades. Topped out at 96mph at 5800rpm. Had a slight prop cav while getting up on plane just backed off throttle a bit, props bit and away we went.
Over the winter we upped the engines to 540's w/ 700hp, moved the engines forward 2', Stellings 12" ext. boxes set at neutral(7/8" up), Imco SC drives, 1.5 w/ -2 shorties. So we're up almost 3" with alot more power.
So far we've tried a 26P Hydro 5 blades. Way too small. Reached 6K at half throttle, props blowing out before on plane, bad porpousing after on plane at 70mph.
Next we tried a set of 34P 4 blades. Still too small. reached 6K at 3/4 throttle. Blow out seemed better and porpousing seemed better. Got to 102mph but boat scary loose in the stern.
Third try with a set of 33 Throttle up 5 blades. Blow out real bad, once it bites it takes off. Great punch at 75 but around 85 starts to porpous again, bad! Think it would go past 102 point but trying to power thru it starts to get real loose and jumping out of the water. Trim doesn't seem to help with any prop.
Knowing that I will most likely have to re-gear the lowers to 1.36? would help with prop pitch selection. I was considering spacing the lowers down 1.5" to see if it helps the looseness at speed and possibly help the blowout? Am I on the right track here? Any suggestions would be appreciated?
Sorry for the long story.