johnmiffco

id be finding out the cam specs,,,of this custom cam
have seen many times motor makes power on dyno
and when put in boat had no balls up high to pull the load
have a bud now with 572s that would turn 5800
and cam change during refresh wont go past 52 with same props
put on 28s and same rpm
try a 23 pitch prop,,if stops at 5200 well,,,,,,,,,,
just a test to try,,,,

Griff

A 40 hp gain is only worth about 2-3 mph on the top end. I suspect your torque is falling off. Based on the 588hp at 5200, torque is close to 588 then as well.

boostedls87

Yeah you are right Griff at 5100 the tq starts to fall off at 599tq. What ideas do you have? I just measured the Prop shaft height for the x deminsion. With the drive all the way down the center of the nose cone to the bottom of the pad is 7" is that pretty deep?

thanks,
Mike

boostedls87

I did notice looking closer at the prop there is some cupping work done to it. This would reduce the rpms a little also wouldn't it?

Thanks for the help so far guys

johnmiffco

the 26 cv is a very nice hull
they also were a descent layup for their days
so not a heavy boat and a good wave crusher
so not pulling a big load for the ci
had 1 here with 500hp 502 with 26p hydromotive 4 blade prop and saw 58-6000 rpms
breaking mid 80s in slop
as stated the torque is falling off way too early
doubt its some cup on a 3 blade 25 prop keeping it from turning past 5200
try a smaller wheel and see if still only goes to 5200

boostedls87

Thanks John,

Did that 26cv you were testing have a stock lower unit on the drive? So if my torque is falling off too early it could just be in the design of the cam and engine setup?

johnmiffco

been over 10 yrs ago it was here
but yes had bravo outdrive on it
as boat was originally raced in a p class
new owner put in the 502 with a little clean up,intake,carb and headers
so 550 hp window as oem long block,,,,
as said,,,my bud just bought his old boat back and was low on rpm on both motors
from when he had owned it before
on tear down couple weeks ago,,,,found different cams in them
over the 1s that they had in it in the past
so as why id check the cam specs against a known cam used in that sized motor
but putting on a small prop is a simple test,,,,if goes to the moon fast,,,,cool,,,,
if stays in 52-5300 window,,,,motor is falling off too much
as timing and cam has lots to do with rpm a motor achieves

Griff

You need to have a paid membership to upload files directly to OSO or you can use a pic sharing site and attach from there.

Try attaching the dyno sheet and post cam specs. If peak torque is at 5100 then it should still have 560lbs+ based on your other posted numbers and spin easily to 5800.
It could be the hull and or drive depth holding it back.

johnmiffco

1 problem u have is u have no data of what the boat was doing before motor upgrade as the new owner
did u ever get any #s before bought it or before motor popped?
hull can be delaminated on the bottom as they were a balsa cored bottom,,,may want to ck that
as I have repaired 1 before from that,,and was that boat that was here
and delam flex can slow it way down
prop depth should be good as they were built for class racing,,,,
whats needed for slop water racing,,,but not low enough to scrubb lot of rpm
raising will help for max speed but take away a tad on small hull rough water handling
complete cv rig is only 3900-4000 lb window and is a nice, fast,good handling low profile hull for its size
but as griff stated would like to see the dyno sheet and cam specs
as also trying a small wheel for reference results

Tinkerer

Is this boat sitting on a bunk or possibly a roller trailer?
Have You checked the last 6 foot of the bottom for any hook.
Put a straight edge that is at least 5 ft long and see if there is any gap between the straight edge and the bottom of the boat.
Don't just check the pad check up to at least the first chine.
I think you have a few things that are adding up to a poorly performing boat.
Engine builders tend to put too mild of a cam in boat engines. You need to be aggressive with boat engine cams