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Old 06-10-2020, 09:24 PM   #1
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Default 4.3l 180hp wot rpm?

I have a 1993 1800sr and want to know the best prop to get for my boat. Looking for quick out of the water and speed. 4.3l engine and should be 180hp, mercruiser alpha one.
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Old 06-11-2020, 01:43 AM   #2
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What is the WOT with your current prop and what size is it? There is a Quicksilver prop calculator you can try to see what it recommends.
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Old 06-11-2020, 02:17 AM   #3
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I do not know. It is a basic prop, prob close to original. I wanted to see what original mfg spec is first. Boat for the most part is original.
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Old 06-11-2020, 11:15 AM   #4
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Ok but still need to know the current WOT. There may be a part number on the side of the props hub, if not remove the mounting hardware and it may be on the face of the hub.
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Old 06-11-2020, 01:16 PM   #5
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The Max RPM range is 4400 - 4800. You need to compare the current performance against that target in order to determine how (IF) you can tune better.

Going down in pitch will increase max RPM and time to plane, but decrease top speed and cruise speed. However going too low (under-propping) can lead to potential over-revving.

Going up in pitch will decrease max RPM and time to plane but increase top and cruise speed. However going too high(over-propping) can lead to overloading the engine and in extreme cases, not being able to properly get on plane (especially when there is increased gear and people load).

So, we really need to know what the current Max RPM is at WOT. Get the boat up on plane, then trim out the drive until it cavitates, then click the drive back in until the cavitation stops. Hold it there for a few seconds and see where Max RPM is. It's best to do this in calm conditions with little chop or wake traffic.
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Old 06-11-2020, 02:17 PM   #6
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I should be taking the boat out this weekend. I looked at the current prop and it is a solace 21 pitch #1511-143-21.
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Old 06-12-2020, 01:32 PM   #7
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correction

Quote:
Originally Posted by shrew View Post

going down in pitch will increase max rpm and reduce time to plane, but decrease top speed and cruise speed.

Going up in pitch will decrease max rpm and increase time to plane but increase top and cruise speed.
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Old 06-15-2020, 02:28 PM   #8
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I took the boat out and had about 650lbs on board. At wot is was about 4800rpm. I was going 41mph (GPS).
Can i get better?
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Old 06-15-2020, 03:04 PM   #9
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Quote:
Originally Posted by georgejlewis View Post
I took the boat out and had about 650lbs on board. At wot is was about 4800rpm. I was going 41mph (GPS).
Can i get better?
WOT for that engine is 4400-4800 and your top speed seems good. WOT is @ test rpm and should not be operated at for more than a few minutes. You can make a prop change but to gain topend the lower performance is impacted and vise versa.
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Old 06-15-2020, 05:51 PM   #10
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Quote:
Originally Posted by georgejlewis View Post
I took the boat out and had about 650lbs on board. At wot is was about 4800rpm. I was going 41mph (GPS).
Can i get better?
Do you mean faster? Yes, you can get more top end by going to a 23P, but, that will slow your hole shot and increase time to plane. The trade off is always top end speed for hole shot performance.
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