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Question about correct prop pitch

R

rcahill31

Regular Contributor
"I have a 1988 four winns 245

"I have a 1988 four winns 245 vista with a 5.7 litre cobra and outdrive, present prop is 15x17, with about 30 gals of gas, and another 250 pounds of gear, six people and after it is on plane and trimmed out the wot is about 3700 rpm's, all filters have been changed, the anti valve is fine as is the vent hose, after talking to sales people about a prop I have been told not to go lower than a 15 pitch which would increase the wot about 400 rpm's, the reason I was told that going lower than the 15 pitch would not perform as well and perhaps could harm the engine by over reving, can you give me your input?"
 
"you'll have to try a 15 a

"you'll have to try a 15 and see...you are doing the engine no favours by lugging it like that...you can cup a valve ...If you are sure the engine is making it's 260HP then go to 15 or 13 whatever it takes to get the WOT rpm to 4200-4600 range. Did it ever perform better? I would be looking at more than just filters. Start with compression test, and then inspect advance weights in the distributor. Plugs, wires all that other stuff....and clean the flame arrester and make sure the secondaries are opening on the carb"
 
"I used to have a 1988 Doral C

"I used to have a 1988 Doral Citation, 25 ft cruiser with a 5.7 OMC Cobra. I ran it with a 15x15 aluminum and I would get into the low 4000's depending on how much gear and fuel, water we carried. The 15 pitch also gave it enough of a hole shot we taught my older son (about 9-10 at that time) to water ski with it."
 
"My cobra outdrive with the 5.

"My cobra outdrive with the 5.7 liter engine had the 15x17 prop and wot was 3500 rpm's, found a 15.5 x13 on e-bay and tried it out last sunday and the wot now is 4300 rpm's, working fine, not a speedboat but for a 1988 4-winns 245 it was not meant to be."
 
"Going down 4 in of pitch is p

"Going down 4 in of pitch is pretty significant. At least we know our rule of thumb of 200 rpm per inch of pitch change is right on in your case
happy.gif
. How was your hole shot? I would expect it to get up on plane fairly quickly with the 13 but your top end speed should also be less now?"
 
"Bob, you are on the money, We

"Bob, you are on the money, We can get up quicker but like you said the top end speed is less so I guess you have one or the other, at least the engine is reving up"
 
I'd be cutting a test hole

I'd be cutting a test hole in the floor of that 4Winns and see what the floatation foam looks like - might be carrying a half ton of water under the floor like so many late 80's boats
 
"it comes up on plane quickly

"it comes up on plane quickly if it had a half ton of water do you beleive it would come up on plane in a short period of time with 50 gals of gas, four adults, coolers of bev, two batt, and etc?"
 
"Hard to say.. probably not, b

"Hard to say.. probably not, but costs nothing to cut a test hole, so I would do that - In fact I've done one on every boat I've ever owned."
 
"Hy, if you cut a test hole in

"Hy, if you cut a test hole in this 4 winns cruiser I assume it would be in the cuddy under one of the seats is this where you would suggest? also when remounting the outdrive after doing some maintenance do you use anything on the outdrive mounting gasket such as a sealer I know omc says to use omc sealer but what does one use in place of a omc product?"
 
"a big hammer and a beating on

"a big hammer and a beating on the floor boards will (by sound) tell you where it's bonded to the stringers and trusses. you want to make a hole between trusses. The cuddy probably doesn't have foam under it, and water would migrate rearward. Just in front of engine compartment best area - under a seat or compartment to hide the cut.
Permatex Ultra Grey is a nice sealant- spreads nice and cleans up nicely. waterproof and oil resistant."
 
"It has a bed just in front o

"It has a bed just in front of the engine compartment I could check and see when I pull for winter but at my age (77) I probably would boat till the end and then sell it, I had a Larson runabout yrs ago that was water logged and it was a job tearing the floor out and redoing it all, thank's again Hy"
 
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