4 cylinder volvo 125hp

[Chevyboi001]

77 bayliner cuddy 21ft. 4 adults speed 20.1knots rpm4400. if I used the online prop pitch calculator I have a 14x15. max rpm is around 5500. so what do I need to do to get it up to rpm and plain faster. up or down on pitch? diameter count for anything?

 

[Starcraft5834]

125hp pushing 21ft boat is a chore...your going to need maximum thrust, a 4 blade prop would be a good start.. as to your engine,,I have a merc 140 3.0 that WOT max is 4800... don't know about Volvo's.. 4 blade will push you out of hole best..

 

[steelespike]

As usual the Volvo is a mystery to most of us. We need the full model number and what it means,Outdrive number and what it means?
I tried to find a prop any prop couldn't even come close.
Maybe I'm a little bit thick.I'm confused. Are you saying 4 adults manage 20.1knots and you alone with a 15" prop is 5500?
Or is it 5500 the wot rpm rating?Do you know your gear ratio?Is your speed by gps?
Can you do a light load test run ,just you, get us the wot rpm and gps speed.

 

[Maclin]

IF the boat is in order, meaning no extra water-logged weight, bottom in good shape, etc.....and if the engine is in tune and just can't get to the top rpm due to prop load then you need to go down to a 12 to get to 5500 and a 13 gets you to 5000. I doubt the the engine is in good tune though because a 15 is pretty low for a 2,13 gear ratio, so a 13p is radical and a 12p, well, may not even be available. When was the last time the engine was tuned? Filters changed? Carbs rebuilt all that

 

[Maclin]

BTW for the rest of us, on his 4cyl engine that is the top rpm range..

 

[Maclin]

Chevynoi001, just to clarify, do you know what pitch you prop is? Or are you guessing based on calculations?

 

[Chevyboi001]

sorry for not being clear.
volvo aq140a (125hp)
280 outdrive
im using online pitch caculator which i could be wrong on sizing.
max wot range of the motor is 5500
4 adults and a cooler we got up to 20.1 knots using gps as speedo.
ive never had the boat out alone
21ft bayliner cuddy cabin
far as maint goes i just rebuilt the engine. new bearings cylinder head work timing belt everything. manifold. i set timing with a timing light 32degrees by 3k rpm
also i think i need to work on my trim angle as it is set all the way down i think bringing it up some would help. ive look on my props (i bought boat with two but p.o told me they are not the right ones says he tore the right one up on a rock. and doesnt remember pitch.) i need a good starting off prop for my prop testing thats what im trying to figure out. i would love to know what prop pitch came stock i could work from there seeing as i dont know where i am now on pitch.

 

[Chevyboi001]

ok so one of my props im sure is a 15x15 michigan smc 341. found the numbers just now. and im gonna try and do the measurements on the other one right now again to double check my findings. really appreciate the help. thank you

 

[steelespike]

If no power trim set it so the outdrive is perpendicular to the water.
If you set the gps for mph it will be a little easier to calculate. Your at 23.13 mph
Is the bottom clean and smooth? no bulges or hollows?or flakey paint?
Are the props thru hub exhaust?Are you sure the timing advances as it should?
Even though it is a recent install don't assume all is right.
A 15" is pretty far down the list With you alone it should over rev.
I think with 4 aboard it should perform nicely.

 

[Chevyboi001]

my timing not all the way advance i set it at 32 at 3k rpm should be at 38 3k rpm. hull is perfect. no paint chips nothing. im going out to test it alone tomorrow with my timing light and tools wish me good luck last time this thing started taking on water fast.