help with some fine tuning of prop

[nailem]

i have a 86' 20' sundowner 220cv with a 5.0l 230hp mercruiser and alpha one drive. i will be doing mostly family cruising with some wakboading.

after finally getting everything else tuned up, carb, plugs, cap, ext. she is running pretty good. my current prop is a 14.5 x 17 3 blade and WOT is running about 4200 RPM and 36mph per GPS. i think the motor should be 4200-4600 or 4400-4800 i have found both specs.

i was think of trying a 15 x 16 4 blade but would this add to much drag and lower my RPM? or do i go to a 16 x 16 3 blade? not really concerned about speed although i dont want to be to slow. what is the opinion of the pros?

thanks in advance

 

[Bondo]

Re: help with some fine tuning of prop

Ayuh,..... I'd go with the 15x16 4 blade....

 

[nailem]

Re: help with some fine tuning of prop

thanks for the advice. do you think that will get my rpms up any?

i really dont get how these props effect different boats. my buddy just bought a 86' 23' mach 1 with the same 5.0l 230hp motor. his boat is a little heavier and he as a 15 x 19 prop and it seems to be the right prop for him. i have to go to a 16 pitch prop to get the same rpms. does not make sense to me.

 

[steelespike]

Re: help with some fine tuning of prop

From your description it would appear there is something up with your boat or motor.Check compression,Did you check timing?Is the throttle opening all the way.Flash supresser clean? Are your prop and friends prop both aluminum?(usually painted).
Your hull may have absorbed water.Is the bottom clean and true?

 

[nailem]

Re: help with some fine tuning of prop

his prop is a ss and mine is aluminum. but from what i have read a ss prop is like adding 1* of pitch to an aluminum. so a 19 SS would be like a 20 AL. not sure if thats true. my boat has bottom paint on it and his does not. i understand the bottom paint adds some drag but i would not think that much. his boat has sleeker lines than mine but again im not sure all that would make that big of a difference.

i cleaned my carb and it is working correctly. the boat does not seem to be water logged but not sure how to tell exactly. it sits at its normal water line and also floats level. my timing is dead on. new plugs, rotor and cap. it does idle a little ruff but i put 87 octane in it and i think that is why. that would be the only other difference is he is running 89 octane and i have 87.

his boat ran 46MPR and mine ran 36MPR. he can not tell what RPM he is at because right now his tach is not working. i do have a digital tach he is going to barrow.

so if i understand you correctly there should not be this big gap between prop sizes between us? i think i may try a 14 3/4 X 15 4 blade solas amita. i can get one from this site for $104 shipped. do you think this will bring my RPMs up with out giving away to much top end?

thanks again

 

[MikDee]

Re: help with some fine tuning of prop

IMO your buddy has a 350 (5.7) not a 305 (5.0), making that heavier 23' boat do 46mph! I had a 24' SeaRay with a 350/260hp, that only did 35mph when I got it, until I added synthetic oil, thru hull exhausts, it had a clean bottom, and lightly loaded with a 17" pitch black max aluminum prop, then fully trimmed out, it just made 40mph!

 

[nailem]

Re: help with some fine tuning of prop

i'll chech is engine tag again but i thought for sure it said 230hp.

so what do you all think about my prop
16 x 16 3 blade or
15 x 16 4 blade or
14 3/4 x 15 4 blade

 

[nailem]

Re: help with some fine tuning of prop

went out again last evening and only got 4000-4100 rpms. thats was with me my wife and my two daughters on board. 1/2 a tank of fuel (15gal) so thats only about 475lbs total. little wind and lake was flat.

anyone have any thoughts on the prop. i called around here (Erie, PA) and no one has any used props or does any kind of trial of props.

if i dont here anything i think im going to try the 14 3/4 x 15 4 blade. im guessing that will put me in the 4500rpm range.

i talked to my buddy and he said the valve cover says 230hp but i guess someone could have put different covers on. i'll check the seriel #. he said again with just him in the boat he got 46mph.

 

[MikDee]

Re: help with some fine tuning of prop

Ok, I went to NADA, and found out your boat is the same weight as my old 79'- 20' SeaRay bowrider with a 305/228hp Mercruiser, and a 14X19 Black Max Aluminum prop, that did 45-48mph fully trimmed out. So, I'd say your engine is not putting out it's full horsepower? and before looking for a prop, you should fix that.

 

[nailem]

Re: help with some fine tuning of prop

thanks mikdee, i know this should probable be move to the i/o forum but.....
im not sure why my hp would be down. i put new plugs, cap, rotor, and oil change. timing was set at idle to 9* BTDC. carb was disabled and cleaned. accelerator pump was in good shape and giving a good squirt of fuel. i think my timing need tweaked a little because i have a slight lag when i hammer down from idle.

things i guess i need to check:
compression, fuel psi...... what else??????

i did use 1qt of 84w140 gear lube and 1/2qt 80w90 when i did the out drive. would that rob that much HP?

 

[MikDee]

Re: help with some fine tuning of prop

That all sounds good but, I had a 4bbl Qjet carb orig. eqip. on my 228hp/305, not sure if you have a 2bbl or 4bbl? An important item to check, is make sure the carb, 2bbl, or 4bbl, is opening completely at full throttle.

I don't think the heavy gear oil is a problem.

 

[nailem]

Re: help with some fine tuning of prop

It is a 4bbl. I will check again to see if the secondary are opening. Would it need to be under load to properly check this?

 

[MikDee]

Re: help with some fine tuning of prop

No, you can check it with the engine off by opening your throttle fully, once in gear,, but you must hold your choke butterfly open first so no linkage interfere's. Once you verify all is good, check it out on the water after it's fully warmed up. If the secondary butterflies don't open, then it's not opening, because they lift the metering rods (in the carb middle) for the secondary fuel jets to open.

 

[steelespike]

Re: help with some fine tuning of prop

I agree something is up perhaps the motor is weak.Are you sure it's firing on all cylinders.Rough idle could indicate a bad valve or no spark on one cylinder. Perhaps trim isn't going up all the way.Have you confirmed full throttle?I don't think a prop is the solution. I would say a 15" prop would be comepletly off the scale in your application.A 4 blade is usually for low end performance and will generally reduce max speed.

 

[nailem]

Re: help with some fine tuning of prop

do i have to be underway and hammer down to check the throttle plates or can i just rev the engine in neutral?

i am going to replace the wires and try to find someone i can borrow a compression tester from. i read the bulletin on how to do it but just checking to make sure do you test with all the plugs out?