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Prop issues need some advice

J

jchris1062

Member
"I have a 1989 21 foot four wi

"I have a 1989 21 foot four winns sundowner. The boat had a 5.0 with a cobra drive. I replaced the 5.0 with a 5.7 310 hp and the cobra that came with the motor.The boat takes a while to plane, turns about 4300 rpms and runs about 36 mph. The marking on the prop is HH517 13, 15X7. I have a S.S. 14 1/4 X 22 that I can try. I do not know alot about props so I thought I would ask someone with alot more knowledge for advice. Thanks"
 
I forget to add that the 14 1/

I forget to add that the 14 1/4 22 was on the dirve when it was mated with the 5.0 when I got the boat. Thanks
 
"The prop specs, as you've

"The prop specs, as you've written them, don't make sense. Assuming your new motor is properly tuned, it should easily rev far higher than the 5.0.

Jeff"
 
"If anything I suspect the 14

"If anything I suspect the 14 1/4x22 is going drop your WOT RPM's down even more, you may see a bit of improvement in top end speed but also a decreased hole shot which you say is already slow. I think you need to go down in pitch to at least 15x15 (or maybe 15x13?), rule of thumb is one inch of pitch will change RPM's by 150-200 so a 15x15 will bring you up to around 4600-4700? You should see an improvement in your hole shot getting up on plane too."
 
"Same drive?
Either an engine

"Same drive?
Either an engine problem or tach problem if the old 5.0 pulled it within the nominated max rpm range of 41-4600 with the 22" pitch, which I doubt!"
 
"fastjeff,
I have an omc 197

"fastjeff,
I have an omc 1978 305 185hp in a 1978 hammond 1725v cordoba 17ft the stock prop looks to be a 15x16 I got the boat with a 15x17 and the rpms were 4400 at full throttle about 44mph Ive changed the prop to a 14 1/2x19 the speed has increased to 46mph but the rpm is only 3600 and the carb is wide open 2bbl is there any way to keep the prop and attain the 4400rpm again maybe 4bbl carb or bigger 2bbl or will I be over working the engine."
 
"Your lugging the engine like

"Your lugging the engine like that which is not good for it. You need to come back down in pitch, I would think your hole shot is suffering too. The extra 2 mph can't be thatimportant?"
 
thats just it the hole shot is

thats just it the hole shot is almost the same is there a reason I can't carb up to get the rpm or am I missing something here thanks for the reply bob
 
"I need to back up a bit, just

"I need to back up a bit, just confirming you now have a 5.7 in the boat, does it have a 5.7 drive or are you using the drive off the 5.0?"
 
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