WOT RPM range for Mercrusier 383MPI

When shopping for one, my dad was told he would have to change the 1.5 ratio drive in a 2350 Chaparral to a 1.65, cause the 383 "will have to rev" to produce it's power. Well, he bought one, but it was delivered without any specs saying what the WOT RPM limit is. And the salesman couldn't tell him excatly what it was either. So does anyone know what the WOT RPM range is supposed to be on that engine? Thank you.

Re: WOT RPM range for Mercrusier 383MPI

WOT is 4800 to 5200 rpm. I would recommend proping to no more than 5000 rpm.

Re: WOT RPM range for Mercrusier 383MPI

Okay, thanks for the info! He's got it at 4600 rpm right now with the prop that was on the 454 Magnum. I think he might try the next pitch lower, and he'll get in the "sweet spot".
Is there any technical specs on that motor somewhere? I may be interested in one of them the next time I buy a boat with a broken small block (or big block!)

Thanks again.

Re: WOT RPM range for Mercrusier 383MPI

The merc 6.2 MPI has a 4600-5000rpm range according to the spec on Merc site. Not sure if this is the same engine, since it is a 377 (not bored 0.030 over to make 383). Maybe merc offers a 383 as replacement only, and does not advertise it.

Re: WOT RPM range for Mercrusier 383MPI

The 383 has a substantially longer stroke (3.75" (same as a 427 big block) vs 3.48") than the the 6.2. To achieve the same piston speed (2900 fps) of a 6.2 at 5000 RPM, the 383 will only be turning 4640 RPM. Running a 383 at 5200 RPM would create the same internal stresses as running a 6.2 at 5600 RPM. There's also a possiblity that it has a shorter connecting rod than the 6.2, and that only exacerbates the stresses.

I think I'd prop it to run 5000, but limit it to maybe 3500 90%+ of the time, if longevity was a concern.

Re: WOT RPM range for Mercrusier 383MPI

John, a 383MPI is a replacement engine from Mercruiser. They are sold as either a complete engine (manifolds and all the accessories) or as a complete power package (engine plus transom assembly and drive). They are a "remanufactured" engine. I suspect that is why I can't find any actual specs or the factory WOT rom range. I believe Reel Poor when he says it's 4800-5200, cause that sort of matches what the sales person told my dad about it needing to rev. I think it's a little odd that a longer stroke motor would "need to rev" more than a shorter stroke engine, but it's not totally crazy. I just want my dad (and my sister) to avoid "lugging" the engine and damaging the valves in the Vortec heads.
MM, a 6.2 also has the 3.75" stroke.
So Mercruiser can be "remanufacturing" two different engines here, either a 5.7 or a 6.2 to come up with this 383MPI.
So does anyone know whether they are taking 6.2s and boring them .030 or are they taking 5.7s and boring and stroking them. And are they really remanned engines, or are they "new" ones that GM supplies and Mercruiser changes? Seems like if they were all new, Merc would sell them as all new and charge more!

Re: WOT RPM range for Mercrusier 383MPI

Thanks for the clarification on the reman. I would think the 6.2L stroker specs are close enough for the 383.

I would try contacting Merc by phone or email, to get engine specs. I have seen installation manuals on the standard engines, which includes main engine specs.

What drive are you using? When I saw the ratios, I thought alpha, but you mentioned a prop from a big block. Are you downsizing from BB to the SB stroker? That might explain the ratio change suggestion. As long as you are in the right rpm range, should be good.

PS: Yep, 6.2L MPI is a stroker too!

Re: WOT RPM range for Mercrusier 383MPI

The boat had a 454 Mag with a Bravo 1. Okay, it might be a 1.49 or a 1.47 ratio, but you all knew what I meant! Yes the switch was made from the BB to the 383MPI. So far it's turning the same prop that the 454 was, (which I think is a 19, but it may be a 21) but the 383s WOT is only 4600. After having issues with the valves in my 1997 5.7, I wanted to make sure that the 383 would not get "lugged" and have the same problem. I think my dad will trying the next lower pitch prop.
The 454 was a little tired, eventually blew headgaskets, and had a bad piston. My dad's initial impression is that the 383 is equal to the 454 in top end, and superior out of the hole. The lower pitch prop will make it even better out of the hole, and maybe won't slow it down on the top end. But that isn't how the boat will be used, low end and the ability to fire it up by just turning the key was the reason for going with the 383.