Engine replacement question

[BarryT]

I have an old 1972 Caravelle with a Mercruiser 215hp Ford 302. Is a Mercruiser 351W of the same year a direct bolt on replacement for the 302? My engine might have freeze damage and if I am going to replace it might as well repower to the 351 if I can. I have heard that the 302 2 barrel the 302 four barrel and the 351 2 barrel and 351 4 barrel were all used the same drive with the same final ratio.

-barry

 

[Don S]

Re: Engine replacement question

Direct bolt in, NO, will it fit and work, YES.

 

[BarryT]

Re: Engine replacement question

I will be buying a remanufactured long block. The 302 uses 351w heads so the intake manifold will be the same. The exhaust manifolds are the same. I know I am missing something.

-barry

 

[coastalcruiser]

Re: Engine replacement question

351 is a few inches wider, so you will need the 351 Y tube

 

[WizeOne]

Re: Engine replacement question

You'll also need a new intake manifold, a new distributor and possibly a new alternator bracket.

How big is your boat?

The 351 is about two inches wider, two inches taller and near a half a kid heavier. Make sure you have the room and want to carry around the extra weight in the stern.

 

[BarryT]

Re: Engine replacement question

Well the ford 302 on the mercruiser has 351w heads and a 351w cam if I am not mistaken so, I believe the intake will fit. Getting an alternator to fit isnt really a big deal. My boat is a 1972 caravelle 21' cuddy cruiser. I could just buy a remanufactured 302 direct replacement and just get a edelbrock camshaft and intake that boosts the idlel to 5,000rp range. That would give me a little extra kick if If I have to put a new engine in.


-barry

 

[WizeOne]

Re: Engine replacement question

.....so, I believe the intake will fit.

WRONG! A 302w intake will not fit a 351w engine.

Your mention of the heads brings up another issue. Yes, your 302 has 351 heads but they were only drilled (by Ford) for the 7/16" 302 head bolts. The 351 block will require 1/2" head bolts and they will not fit thru your heads.(machine shop time) But I think you mentioned acquiring a long block, in which event, you would not be reusing your 302 heads.

You also want to make sure that long block has all brass casting/freeze plugs.

That brings up another difference. The oil pan is different, won't swap!

Take it all or leave it. You would find out soon enough.

 

[BarryT]

Re: Engine replacement question

So is my intake manifold a 302w or a 351w intake manifold? I will be buying a long block as stated above it will come with heads. I am talking about intake manifold fitment. If the 302 has 351w heads a 351w intake manifold should fit. yes or no?


-barry

 

[WizeOne]

Re: Engine replacement question

A Marine 302 with 351 heads uses the same intake as a std 302. It will not fit on a 351 engine with 351 heads.

I also added above, after you posted, "You also want to make sure that longblock has all brass casting/freeze plugs."

If your longblock comes with an oil pan you want to make sure it is the right config. Your 302 pan will not fit.

 

[BarryT]

Re: Engine replacement question

The engine will be from a marine shop. it will have all brass plugs and what not. Since I would need a new intake distributor and y pipe for the exhaust I think I might just go witht he direct replacement marine 302 and maybe put a better came and intake on it to get a little boost. I really hope my original engine isnt fubar'd, but it very well might be. The cam that is in the 215hp mercruiser ford 302 is it a 302 cam or a 351w cam. I am asking becauae a another post said it was a 351w cam.


-barry

 

[WizeOne]

Re: Engine replacement question

There is not much you can really do for a cam upgrade in the 302. You have little leaway in not creating a problem with too high an idle (shifting problem), too high a torque curve or a lobe seperation issue that would suck water into your engine. (reversion) The cam you have is a 351 firing order cam.

As far as a better intake, the only choice you would have would be an Edelbrock Performer intake (or equivelant), not a Performer RPM. Once again the RPM version would move you power curve much higher that you want in a marine engine. You'd hit the throttle and it would fall on it's face. Especially with a heavier larger boat like yours. The other issue is that if you boat in salt water, forget an aluminum intake unless you go to closed cooling

One thing you can do is to make sure the new 302 has a 9.0:1 compression ratio instead of the stock 8.0:1

Or better yet you could get a stroked, to 331 ci, shortblock. Now you'd be talking some serious extra poop (along with reliability) with out the size, weight and new parts issue of a 351. You'd want that with a 9.0:1 compression ratio as well and you can still run 87 octane regular.

 

[BarryT]

Re: Engine replacement question

Ok cool, thanks for the help. Edelbrock sells a cam just for the idle to 5,500rpm range. I would think that would be perfect, but I am new to boats.

-barry

 

[WizeOne]

Re: Engine replacement question

Ok cool, thanks for the help. Edelbrock sells a cam just for the idle to 5,500rpm range. I would think that would be perfect, but I am new to boats.

-barry

Reread my entire post above. I added to it.

As for the Edelbrock marine cam, it would not differ from what you have, or at least so little that it is not worth the money. The intake, however, would be worth it if you do not run in salt.

 

[BarryT]

Re: Engine replacement question

I will only using it in freshwater in the forseable future. If my block wasn't destroyed by the freak freeze that we got then I will get and intake and maybe a head port and flow or something just to refresh the engine a little. If it is damaged well I will just buy the remanufactured 302 longlock.

-barry

 

[WizeOne]

Re: Engine replacement question

I had a 302 marine freeze as well. Didn't stick the pocket screwdriver up into the drain holes. All the water did not come out. It took two exhaust manis and cracked the block right across the #'s1 and 2 cylinder. It was a high hour 302 that ran like a swiss watch and didn't use any oil. Grrrrrrrrrrrrr!

 

[BarryT]

Re: Engine replacement question

I cracked one exhaust manifold witch has been replaced. As for right now I don't know the status of the block. I don't think there is any water in the oil. I might be lucky, but who knows. 4 out of the 6 plugs on the block popped. The head's plugs didn't pop. I will only know where I stand after an oil change (looking for water) and freeze plug replacement and running it on the garden hose to see if the it runs like crap or the oil gets milky. Unless you suggest a better way to check for damage. If I have to get a new motor I plan on buying the new engine from rapidomarine.com


-barry

 

[WizeOne]

Re: Engine replacement question

Unless you suggest a better way to check for damage. If I have to get a new motor I plan on buying the new engine from rapidomarine.com

No, running it will be the simplest. I would do it in two stages though. Start it up and just run it long enough to get it to idle. Then shut it down and check the dipstick for milky oil. If it looks ok, then run it again, attempting to get it up to thermostat opening. Keep checking the dipstick as you run it. If there is any sign of milkshake, shut it down and get the oil drained.

I've heard it said, however, that nothing is certain until you get it out and under load, so be cautious if the engine passes it's first tests. Not to be pessemistic but I would not hold my breath, even on the first go around.

On your rapido marine engine, to keep things simple I would stick with the flat tappet 302 not the 5.0 that is pictured on their site. You'd have to change flywheel and front damper otherwize. I would also see if they offer any choice on the compression ratio. The 5.0 pictured appears to have flat top pistons. If that is the case and they use the same pistons in the 302, that would put you up toward the 9.0:1 c/r. Your current engine most likely has dished pistons in it giving it the lower c/r.

 

[BarryT]

Re: Engine replacement question

Rapido marine offers the 1970's version of the engine and that will be the one I am going to purchase. If my engine is trash.


-barry

 

[chiefalen]

Re: Engine replacement question

Have you checked out Michigan motors ?

 

[BarryT]

Re: Engine replacement question

I don't see I list of engines they offer.

-barry