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Discussion Starter · #1 ·
Hey all,

Its been awhile since I posted, too busy boating or working.

I have a 24' Four Winns Liberator (overweight deep-V). The original motor (350 mag) would spin a 17 pitch quicksilver stainless prop to 4600 rpm.

I built a fairly stout 383 that would spin the same prop above 6000, or a 17 pitch Mirage Plus about the same. The quicksilver would ventilate or spin out above 4800, where the Mirage plus would still dig.

Thanks to a wayward wingnut, I now have one of those Merc 383 MPI motors (350 gross HP, 325 Prop HP). This motor will only spin the quicksilver prop 4100-4200 RPM, and at that level it sounds like it ventilating. The boat still comes out on plane quick, even without the help of the tabs. At first I thought the ECU was rev limiting the engine at that RPM, but I can spin it to +5000 RPM in neutral.

The only thing different with the setup is I added a transom mount seawater pickup. It rides about 1/2" below the bottom of the boat.

Any ideas? I know this motor is about 100HP off of my old 383, but it should blow the doors off the old 350 Mag.

Thanks in advance,
 

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Discussion Starter · #3 ·
SweetEmotion said:
I didnt know the 241 came with a 350? Seems alittle underpowered to push a 24ft Libby. Why didnt you go with a big block? :confused:
Alpha drive, plus I thought I had another 383 laying around, which was actually junk (cracked crank and block).
 

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Discussion Starter · #5 ·
Nope, just a single alpha that had a 350 Mag on it when I bought it. It might of originally had a 454/Alpha combo.
 

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Yeah thats true, it would make more sense to swap out the alpha then the 454. Whats ur top speed? Im pushing 61 with my 454mag bravo1
 

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Discussion Starter · #7 ·
Right now with the 17 pitch only turning 4100RPM its not going over 40.

The old 383 pushed it above 60. The 350 Mag pushed it around 45.

I am very concerned about this, you shouldn't have these problems with a new (now 1 yr old) crate mercruiser engine. 28 hours on it.
 

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jherb388 said:


This motor will only spin the quicksilver prop 4100-4200 RPM, and at that level it sounds like it ventilating.

The only thing different with the setup is I added a transom mount seawater pickup. It rides about 1/2" below the bottom of the boat.
How close to the drive is the pickup? Could be causing cavitation of the prop?
 

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Discussion Starter · #9 ·
Re: Re: Merc 383 - 4 Winns 24' Liberator Prop Question

kjo43 said:
How close to the drive is the pickup? Could be causing cavitation of the prop?
This is my best guess too, either that or a fuel pickup issue.

It is a transom mount, mounted about 12" to the right of the gimbal assembly. I will try to grab a pic tonight of it on the lift.

I put it where it looks like on other boats. Should it be level with the hull bottom or even slightly above?
 
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