How should this setup perform?

[jrocksho]

I have a '85 Performance thruster 15' bass boat w/ '85 merc in-line 6 115 H.P.
I have a 22p turbo S.S. prop w/ factory cupping and a 7" jack plate. Prop shaft is appox. 2-3 inches below, cav. plate is 11/2" -2" above bottom. Top speed is around 48 MPH at 4800 RPM by myself w/ fishing gear. I'm not getting the bow lift I think I should. My tach may not be accurate, how can I test my tach? I drilled my holes out slightly bigger on prop due to poor hole shot, but now it seems to cavitate where it is now, if I lower engine one notch, it doesn't seem to lift much and dredge water!! I can't find my happy spot. Anyway, does anyone think I'm asking too much out of my engine, or should I be faster and higher out of water? My RPM to MPH doesn't seem to calculate correctly either. Should I be able to see cav plate at WOT? I'm also below sea level in Louisiana, if that matters any.
Thanks in advance

 

[Dhadley]

Re: How should this setup perform?

Which 22 Turbo do you have? Has it been reworked? What shape is it in?

 

[jrocksho]

Re: How should this setup perform?

I just got it pitched down to a 22p 2 months ago. It was originally a 24p. It is in new condition redone by a turbo dealer. Boat used to run 51 MPH when i bought it, but it was rotted (transom,stringers, and floor). All rotted wood was replaced. Since then it was bogging down out the hole and putting back on trailer. The reason I drilled my vent holes is I bought a laserII 20p prop to try out, it seemed to run same RPM's but lost 3-5 MPH with awesome hole shot, but even less lift. So I got the turbo pitched down.

 

[xxturbowesxx]

Re: How should this setup perform?

i would consider lowering the motor a little and that may allow you to trim out and get on the back pad of the hull.. id guess you should be running 55-60..do a compression test..id also try a 21p 3 blade ss prop..

 

[QC]

Re: How should this setup perform?

You do lose some efficiency when "pitching down". Also, how much weight gain did your repairs introduce? Seems like part of your answer is in your before and after results . . .

Tach verification can be done with a phototach and a piece of reflector tape (what a phototach reads) on the flywheel.

 

[jrocksho]

Re: How should this setup perform?

My compression is 125-130 on all cylinders. Where should my cav. plate be while running WOT? above or below water? Also my boat probably is heavier than before. I added a stringer in the center, instead of going back with the small pieces of wood from factory that run down the middle of hull. I used a
2"x12" board and notched it for the gas tank and floor, plus the transom is slightly thicker than original. I have tried a 20p pro, but it is a laserII. It doesn't perform like a turbo. I'm trying to get more speed with less boat in water. It feels okay when riding alone, but when I have a partner it doesn't lift as much. Thanks

 

[LORDY611]

Re: How should this setup perform?

It feels okay when riding alone, but when I have a partner it doesn't lift as much. Thanks

This plus your earlier statement about beefing up the stringers and transom point straight to more weight which translates into riding lower and going slower. You may be able to calculate your way around it with various pitch props, but the fact is you are asking your motor to push a heavier rig, and it wont perform as if the weight weren't there..