305 to 350 repower need new prop 23p-24p 4 blade 3 blade

[bgiese]

have a 1985 Chris craft scorpion 186 that was a 305 2brl 1.81 out drive
installed a 2001 350 indmar has a Malibu/indmar intake 600 Holley 4brl
a 21 pitch 3 blade prop came with the boat ran 4400 wot with 305 and trimmed up, with the 350 it would go over 5100 wot and could not raise the trim off the bottom due to bow hopping and rpm , borrowed a 24 pitch turbo prop ran around 4200-4300 still couldn't raise the trim much due to the bow hopping but could get the rpm up to around 4500 wot, looking at a 23 pitch 3 blade or a 22 pitch 4 blade to try to get the rpm into the 4600-4800 range (not sure of the correct rpm for this motor havn't been able to find any documentation for this application, what do you all think would a 4 blade help lift the bow and keep it up the 3 blades didn't seem to have the lift that i needed. the boat is heavy somewhere between 2700-3500 lbs. thanks for any input

 

[180shabah]

Re: 305 to 350 repower need new prop 23p-24p 4 blade 3 blade

The 350 weighs the same as a 305 - your original prop should have performed the same except for speed/rpm at the top end.

You have added 75-100hp and increased speed accordingly.

Have you verified that the hull is straight and true?
No hook?
No rocker?

 

[180shabah]

Re: 305 to 350 repower need new prop 23p-24p 4 blade 3 blade

1.8 drive on a v8 - are you above 5000 feet?

 

[bgiese]

Re: 305 to 350 repower need new prop 23p-24p 4 blade 3 blade

the difference with the 21 pitch prop was the higher than recommended WOT
it was running at 5100-5300 was my understanding that I should be around 4400-4800 with the new motor, what really is a mystery is why all of a sudden
my boat wants to porpoise when I try to bring the trim off the bottom, with the old motor/prop it wouldn't do that, I could trim it up and get a good speed run, which is the reason for the 3 blade vs the 4 blade question, was wondering if the 4 blade would help with the lifting the bow, the outdrive ratio was taken from the decal on the replaced lower and I could be wrong I was typing from memory, the manual says it could be 1.62, 1.65, 1.81 , the 24pitch dropped the rpm down to around 4200-4500 and as long as I don't bring the trim up very much will not porpoise but if I raise the trim up it seems to jump around considerable just looking for the best possible prop pitch
thanks for any info