1995 Omc 302 replacement to 351 help

[Scott1971]

I have a 1995 chris craft with a OMC 5.0 302 ford. I’m thinking about replacing it with a 5.8 351. Does anyone know if this is going to be a big job? Will the Y pipe from the 5.0 work? Will the accessories and brackets on the front of the motor bolt right on to a 5.8?
Would this be a direct bolt in replacement motor? I know the 5.8 will be a couple of inches taller.
thanks Scott

 

[Horigan]

Nice boat! I'm curious on this as well. I suspect you may need the ECM for the 5.8 to provide the correct fuel ratio, but am interested in what the experts here will say.

 

[Scott1971]

Thanks buddy! Looks like you have the same boat? I look forward to to hearing what people have to say about my post. I would like to start finding parts soon, if the upgrade can be done

 

[kenny nunez]

If your current engine is fuel injected you will be a lot better off going back to a marine Holley carburetor and a standard marine distributor.
You should be able to re connect the exhaust. I am not sure about the flywheel balance, the drive coupler should be no problem as well as the mounts, pulleys. The power steering mount might work. Electrical depends if your 302 is fuel injected you will need to make up a harness, if it is carbureted then the harness and senders will also work.
The 351 with a 4 barrel should produce around 340 hp.
I will try to find out about the flywheel interchangeability.

 

[Scott1971]

Thanks for all your help!
The 302 is carbureted. I was thinking about buying a 351 long block. I know I would have to buy a intake and carb. Does it need different sensors because of the bigger carb?Do you think the 351 has the same mounting width as a 302? Will it bolt right into the same holes?
Sorry for all the questions, but I appreciate the help!

 

[kenny nunez]

The mounting points to the stringers are the same as well as the rear bolt pattern. Be sure to use a dual plane intake manifold and a real marine carburetor.
Summit has both Holley and Edelbrock. The 351 has a larger oil pump drive rod than the 302 is why you need another distributor.
If your exhaust manifolds are good just re use them. Do not forget to install brass core plugs.

 

[Scott1971]

I really appreciate all your efforts! I’m pretty confident about going to the bigger engine now.
thanks

 

[kenny nunez]

There are some different weighted flywheels depending on wether the rear main is a full circle 1 piece seal or the earlier 2 piece. It appears that from 81 on Ford made the block with a full circle 1 piece seal.
Try to find a 351 from a truck that has a manual transmission and from 96 on they also had roller cams. So I guess the best thing to do is to find one in a salvage yard and rebuild it. If you can only find one with an automatic then find out what weight balance does the flywheel haBe. Either 28 or 50 ounces.
I see where some new flywheels from aftermarkets like Summit, Jegs, and some others advertise flywheels with bolt on weights that will work on any Ford 302/351.

 

[Scott1971]

I was thinking about getting a totally rebuilt long block from a place to mostly does marine engines. The upgrade to a 5.8 is what I think is perfect idea. I will check out the flywheel situation and pricing before I buy the motor. This truck motor build does sound pretty interesting. I bet it would make some nice HP. My boat would hit 60 mph for sure lol.

 

[matt167]

Waste of time.. You either need to get a marine 351 cam, the 351W is wider, you may need specific manifolds, not sure about that 100%... All to gain, a few hp, and by a few, I mean by 20-30hp.

Now if you really want to do something cool, you can put GT40 heads on a 347 stroker, marine 351W camshaft, and you can do that in your garage pretty cheap. It'll make a little over 300hp and you'll just end up with a nice fresh engine. You can use any truck block from '93 on and get a roller camshaft. Blocks since '88 or so were machined for rollers but only Mustangs got them early on

 

[Scott1971]

The other gentleman said similar to the same thing. 300 hp does sound nice. So I just want to make sure I have this right.

302 block from a 1996 or newer

Buy a 351 cam and roller lifts and rockers kit, might aswell get the double roller chain aswell with that.

I would probably need a 4 barrel carb and intake?

GT 40 heads, from a early mustang?

Do you think think all the mounting holes are the same on both blocks? I want to be able to put the motor mounts on and all the accessories on the front and drop it right into the boat?

thanks

 

[matt167]

A 1993 1994 or 1995 block works as well. GT40 heads used in Lightnings and 1996 1997 explorer 302

 

[Redrig]

Dont quote me on this as I have not seen it first hand.

But a gent here on Iboats was claiming that GT40"P" heads will work as well. On cars and trucks those are no-no based on the exhaust manifolds , but this gent was claiming with marine exhaust manifolds it made no difference and he could get to the spark plugs just fine with P heads.

The reason I bring that up is that many claim that those "P" heads are better than the regular gt40s. Just food for thought as the P heads are everywhere.

 

[kenny nunez]

I have a friend who rebuilds the high horsepower engines for the Poker Run crowd.
He also balances these engines, he said that whatever engine you get be sure that it comes with the original harmonic balancer and flywheel.

 

[matt167]

Dont quote me on this as I have not seen it first hand.

But a gent here on Iboats was claiming that GT40"P" heads will work as well. On cars and trucks those are no-no based on the exhaust manifolds , but this gent was claiming with marine exhaust manifolds it made no difference and he could get to the spark plugs just fine with P heads.

The reason I bring that up is that many claim that those "P" heads are better than the regular gt40s. Just food for thought as the P heads are everywhere.

They are better, as long as you can get manifold/ headers to fit.. If that is the case they are easier to find, as they were used 1998-2002 on Explorers

 

[Scott1971]

I have a friend who rebuilds the high horsepower engines for the Poker Run crowd.
He also balances these engines, he said that whatever engine you get be sure that it comes with the original harmonic balancer and flywheel.

I guess the engine would have to be a manual transmission. I don’t think the automatic flywheel is tuff enough. And the flywheel on my 302 looks like it’s something that a clutch would bolt to. If that makes any sense lol

 

[Scott1971]

They are better, as long as you can get manifold/ headers to fit.. If that is the case they are easier to find, as they were used 1998-2002 on Explorers

I did a little research looking for the gt 40 heads on ebay. And I did see someone selling heads from a explorer. Now I know why, I will have to see if I can find it again

 

[matt167]

You can bolt a flywheel to any 302.

FWIW, 1996-1997 Expolrers and the OBS body style Ford Lightnings got GT40 heads, along with SN95 Mustangs.

GT40P came in 1998 and ran to 2002 but were only available on Explorers

 

[Redrig]

I did a little research looking for the gt 40 heads on ebay. And I did see someone selling heads from a explorer. Now I know why, I will have to see if I can find it again

The standard gt40s have 3 vertical bars on the front of the head. The P heads have 4 vertical bars

 

[Scott1971]

Another quick question, what size of carb will be needed? Would a 650 cfm be big enough? Then mess around with the jetting to fine tune it ?