OMC 351W to Merc 454

I've been reading this forum for some time . . . should have been doing that before I bought my boat.

I've got a 1992 Chris Craft Crowne 252 with an OMC 351 King Cobra motor and outdrive. The motor had some unknown number of hours on it when I bought it, probably around 350 or so. I stupidly bought the boat with it in the water and, again without educating myself enough. At this point it's apparent that the boat spent some time in salt/brackish water, the outdrive is pretty corroded and it was winterized improperly at some point. The end result is that I've got a motor that I pulled 8 gallons of chocolate milk out of 2 weeks after having it in the water for 2 weeks.

I'm pretty set on buying a new motor/outdrive/transome assembly for this boat. What I'd like to do is to buy a mercruiser 454 and a bravo III. I know that there are folks that have gone from a ford 460 OMC to a mercruiser 454 . . . I'm feeling unsure of the motor mount situation.

Any help you all can provide is very much appreciated!

Re: OMC 351W to Merc 454

I'm pretty set on buying a new motor/outdrive/transome assembly for this boat. What I'd like to do is to buy a mercruiser 454 and a bravo III. I know that there are folks that have gone from a ford 460 OMC to a mercruiser 454 . . . I'm feeling unsure of the motor mount situation.

Click to expand...

Ayuh,.... While it's all pretty much a Plug & Play swap with what you have,...
There's Always adjustments that need alittle Tuning, or whatnot....
Moving the front motor mounts shouldn't be any kinda Big Deal,... Just alittle glass,+ wood...
It's All part of the process,....
Swap the Transom Assembley,... It's mounting determines Everything after it's set....
Slip an alignment bar through it,+ hang the motor off a crane to determine Where the motor mounts need to be,....
Build the mounts, drop in the powerplant, hook it all up, mount the drive, + Go Boatin'...

Re: OMC 351W to Merc 454

my 1984 wellcraft 26ft crusier was repowerd with a 1996 7.4 bravo3 and it hauls *****. I bought her that way. sorry no help here.

cruise 3500rpm 28mph tabs & trim up
wot + 43mph
my boat is very heavy- yours may run better- good luck

Re: OMC 351W to Merc 454

Fairly easy swap as Bond-o points out, just realize and accept the cost, not gonna be cheap. 'nutcase

Re: OMC 351W to Merc 454

Of course I realized that this was not going to be a cheap thing to do but I've been looking around for a nicer boat and even if I forget what I've spent on the boat already the cost seems to be worth the end result.

So now that you all have confirmed what I suspected would be the case as far as motor mounts and the endless list of little bits and pieces I do have another question.

My boat is a 27 footer, weighing in at about 5200lbs. If I put in a 300+ HP mercruiser 454 how do I decide what gear ratio stern drive I should look for? I've seen charts that give some insight but never anything that gives me all the pieces.

I can't tell everyone that visits this forum on a regular basis how helpful your very deep knowledge has been. I went from feeling like I knew nothing about boats when mine developed these issues to at least having an inkling of what I should be doing.

Thanks a million!

Re: OMC 351W to Merc 454

I've seen charts that give some insight but never anything that gives me all the pieces.

Click to expand...

Ayuh,... Which pieces are you Missing,..??

I think the B-IIIs run alittle differently than the B-Is, or Alphas...

Re: OMC 351W to Merc 454

Ahh....another happy OMC Boat Anchor Owner!


As Bondo indicated, it's a "Plug & Play" swap. You will have to drill a couple of extra (bolt) holes in your transom. You should also take the opportunity to inspect your transom carefully for water intrusion and rot as well as looking your front engine mounts over closely.

I removed the OMC (340HP) 460 King Cobra and replaced it with a 1997 (330HP) 454 Bravo III & 1.81:1 drive.

I run it with 26p props and at 4600 (rated) RPM it goes about 57mph.....Because of the Bravo III, it just Rockets out of the hole far better than it EVER did (even when new) with the previous, similarly powered single prop Cobra.

My 87 211 Liberator weighs about 2900lbs + the 1200lbs of engine and drive.

Your boat is heavier of course, so you may want to consider either a 2.00:1 or 2.20:1 ratio in the Bravo III. It will absolutely need to be a 2.20:1 if you get a 300hp 5.7L MPI or 6.2L 320hp etc. You'd probably be ok with a 2.00:1 with a 454. A 1.81:1 drive like I have would probably be way too "tall" for a big cruiser.

I bought the complete package from a damaged boat that included the complete electrical harness. While you could probably use the OMC harness, it may be short a couple of wires. the OMC connector will plug into the Merc engine harness but you'll probably be missing a couple of pins one of which would be the alarm circuit

The steering cable in your boat will connect to the Merc power steering unit.

The drives are dimensionally similar and the placement in the cutout is the same.






It's a fairly easy swap, more HP is better of course and if you can find an MPI engine, while it will cost more, you'd just LOVE the way it runs!

About a year after I finished mine, I found a nearly new low time 496HO/Bravo III for about $8000 locally. I wish I had gotten it!!!


Cheers,


Rick

Re: OMC 351W to Merc 454

Thanks both for the replies.

Right now I'm in the early planning stages here. Keeping my eyes open for motors and stern drives for sale. I'm in a pretty isolate part of upstate New York so it's hard to find parts locally used but I'm going to have a couple of the local boat yards know what I'm looking for.

The info on the gear ratios is definitely helpful. It's sounding like 2.00 to 1 or 2.20 to 1 is the way to go with a 454. That being said I've seen a couple of 8.2 litre motors for about 4.5 or 5k so I may end up going that way. I do have some questions about the amount of HP that a B3 will handle. Are there differences in generations of the outdrives? Should I be careful about a newer motor, i.e. newer than 2000 with any particular outdrive generations?

As it stands right now I have a pretty good idea what the cost is going to be . . . which is a lot;-) So I'm just trying to come up with exactly it is a want to put in the boat. Given that the boat is out of the water and shrinkb wrapped right now I've got a few months to think about this stuff and to start buying parts which is a really good thing.

I'm really looking forward to actually boating next season.

Josh

Re: OMC 351W to Merc 454

If I could get my hands on an 8.2L engine I would buy it right now. The Bravo III will handle that engine quite "handily"!

The Bravos in general are good for around 400hp in round numbers. The highest rating of the newest engines is 425HP.

I think in general you can easily bolt any stock Mercruiser engine to any Bravo drive. It's when you "trick" it that you have to do things like drive showers etc... You don't need to worry about it on a boat like you have. Even when you put the 8.2L engine on a boat that big, you're not going to get a HUGE increase in top speed. It will getup on plane a lot quicker and will probably not burn a LOT more fuel than the other one did at about the same speed...... I would also look for a closed cooled engine too if it were me. (Most of the newer ones are I think)


Have a look at ebay too. You can buy a brand new drive for about $4000 or so and a transom will be around $1500-2200. There's always a LOT of Bravo stuff on ebay.....new and used.... I was lucky. I paid $5K for the engine/drive/transom + all the hardware, harness, gages etc... Those deals are out there......