Merc 383 - 4 Winns 24' Liberator Prop Question

[jmherbert]

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,