Mercruiser swap

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seasalt35

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Jul 29, 2007
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Hi all I am new , I have a 1977 merc 898 302 now a boat anchor do to water in the crank case , can i swap out with any GM mercs without changing out my merc out drive thats currently with the boat ? I kinda thinking about down sizing for better fuel useage , and how much will match up? I know i might have to fabricate for new motor mounts
 
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Uraijit

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Re: Mercruiser swap

The drive is the same, but that's about the ONLY thing that's the same.

You're going to need new exhaust manifolds and elbows, bellhousing, transom plate, new starter, intake, distributor, alternator, water pump, coupler, etc.

You're looking at a very large bill just to swap engines.

Just get another 302, and put it in there.

If you want a Chevy, sell this boat, and buy one with a Chevy in it.
 
achris

achris

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Re: Mercruiser swap

Hmmmm --- 898 was a GM 305... The Ford 302 was an 888... Which one have you got?
 
MikDee

MikDee

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Re: Mercruiser swap

achris said:
Hmmmm --- 898 was a GM 305... The Ford 302 was an 888... Which one have you got?
Click to expand...

Precisely! The Ford has a distributor in the front of the engine, The GM has the distributor in the back. Also, the Ford has spark plugs sticking out of the heads at an angle, and the GM has them sticking out of the heads completely straight. What GM engine are you planning to put in?
 
chiefalen

chiefalen

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Re: Mercruiser swap

If it's a gm than a 350 would fit more gas to burn.

Don't know if a 4.3 has same motor mounts.

Better on the gas new one 220hp ? Thats a question guys. What is the hp for a new 4.3.

Or a older one? 205hp?
 
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Uraijit

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Re: Mercruiser swap

The older 4.3s were rated for everything from 175 to 205 hp...

And yes, if it's the 898, it should've been a 305. The 888 was the Ford. I assumed that he knew it was a Ford engine...

A repower from a 305 to a 4.3 would be much simpler, but I'm not sure what all would remain the same.

I'm assuming that the bellhousing and transom plate would stay the same.

At the very least, new manifolds and distro... I think the mounts are the same. Starter and alternator should be the same, coupler should be the same...

The drive would need to be re-geared for sure.
 
S

seasalt35

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Re: Mercruiser swap

Thanks for all the reply's I heard this sight was full of info I am sorry for the misunderstanding I have a 898 305 its a gm, bottom line momma not to happy with me buying this boat so looking for the cheapest and easiest way to get the ol girl going and i don't mean the wife ha ha:D thanks for all your help.
 
achris

achris

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Re: Mercruiser swap

There are literally millions of old 305 truck engines kicking around out there... You should be able to pick one up for almost nothing... Just swap all the marine bits across and you're in business... :D:D:D

305 and 4.3 mounts are in different places... Everything else is good to go (except exhaust manifolds) and the new 4.3 MPI makes 220hp at the prop! The older 4.3 4bbl was 205hp at the crank and the 2bbl was 175hp at the crank...

Chris......
 
ne7800

ne7800

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Re: Mercruiser swap

Cheepest way would probably go to junk yard and find a decent runing 305 swap all the marine parts you can probaly pick up a used motor for a couple hundred bucks
 
MikDee

MikDee

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Re: Mercruiser swap

You might as well put a 350 in it now, it's not gonna cost any more? But be sure to get the right matching year, same generation motor.
 
f_inscreenname

f_inscreenname

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Re: Mercruiser swap

Or you could find the Holy Grail. The Chevy 400ci. Got to love that longer stroke.:p
 
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Uraijit

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Re: Mercruiser swap

Yeah, while you're at it, go ahead and gold plate it... :rolleyes:

If you can find a 400 for a reasonable price, go for it. It's gonna be wasted on an 'Alpha' setup though, since even a mediocre 400 build is going to put you over the 300HP limit of those drives. ;)
 
achris

achris

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Re: Mercruiser swap

Back in 1986 and 1987 they put a 330hp big block in front of an Alpha....

Chris...........
 
achris

achris

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Re: Mercruiser swap

Uraijit said:
Aye. Care to take a guess at why they stopped? ;)
Click to expand...

The other fact here is that the Bravos weren't introduced until 1988...

I'm not speculating on anything, just presenting the facts... ;)

Chris........
 
U

Uraijit

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Re: Mercruiser swap

achris said:
The other fact here is that the Bravos weren't introduced until 1988...

I'm not speculating on anything, just presenting the facts... ;)

Chris........
Click to expand...

There's a strong correlation between those two events.

They tried the bigger power engines behind the Alphas, and realized they needed a stronger drive for those stronger engines.

Not saying you CAN'T put a 400 in front of an Alpha, but I don't think it'd be worth it. A decently built 400 will be putting out closer to 400 HP min. If you are going to go to the expense of building a 400 though, you'll probably want to do it right, and be doing closer to 500+.

I wouldn't even let a good 400 LOOK at my Alpha. ;)
 
f_inscreenname

f_inscreenname

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Re: Mercruiser swap

Uraijit said:
Aye. Care to take a guess at why they stopped? ;)
Click to expand...

Because people have a tendency to slam boats into gear. I've known a couple of folks over the years that Alpha's behind Big Blocks. For that matter I have a 454 in front of my Volvo 270 outdrive. It's all on how you take care of them.;)
 
M

mtnrat

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Re: Mercruiser swap

OK, now I see that you have a 305, the easiest and cheapest and most available replacement is a pre 1985 2 piece rear main seal 350. I did this exact swap. More power, same fuel use. I got a rebuilt long block for pretty cheap, or you can find a used running truck motor. For a used truck motor you will have to change the freeze plugs to brass. The used truck engine is likely the cheapest way to go and the easiest swap. Everything from you 305 will work.
 
Haut Medoc

Haut Medoc

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Re: Mercruiser swap

mtnrat said:
OK, now I see that you have a 305, the easiest and cheapest and most available replacement is a pre 1985 2 piece rear main seal 350. I did this exact swap. More power, same fuel use. I got a rebuilt long block for pretty cheap, or you can find a used running truck motor. For a used truck motor you will have to change the freeze plugs to brass. The used truck engine is likely the cheapest way to go and the easiest swap. Everything from you 305 will work.
Click to expand...
I agree, go up to the 350, you won't be sorry....
The fuel difference is negligeble....;)
 
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