5.7 mercruiser engine swap

Joined
May 27, 2016
Messages
18
Been reading for 3years and its been extremely helpful but now I've got a big problem and some questions. I got a 20' Marlin Cuddy with a 1990' 5.7 mercruiser sbc, alpha1 gen 1 outdrive. TB 4. Started it up this year and bam water intrusion! Cracked block...bad. Same week a friend is getting rid of his old camper / rv with a 96' small block chevy in it. Score! I think...has only 10,000 ish miles. Im wondering any do's or don't i should be looking out for???
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
40,581
Howdy

There are not as many folks here then normal, most are enjoying the holiday. I'll give ya my thoughts.
The blocks should direct swap, the 1996 should have vortec heads so it will use a different intake manifold. Your carb may or may not fit on the newer motor but you cannot use the automotive carb. Don't use the starter, carb, alternator, circulating water pump or distributer of the newer motor, use the one off your old motor.

Change the core plugs (freeze plugs) to brass, and if your not in salt water you should be good without changing the head gasket.
 
Joined
May 27, 2016
Messages
18
Thx alldodge. I haven't even looked at the rv motor. I am in salt water so i gotta change the head gaskets as well i assume i need a new Marine carb. Everything im hoping will bolt on i.e pwrstr pump, alt, starter and water pump from my mercruiser. I hope my flywheel will go on the newer motor. My question is will my pre alpha handle any added horsepower added by the newer heads....if any???
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
40,581
The flywheel is the same, as for the added HP there isn't enough to worry about with your drive
 

thumpar

Admiral
Joined
Jun 21, 2007
Messages
6,138
The Alpha is good for 300hp as per Mercruiser. There are lots of people that run much more. If you end up with a 4bbl carb Vortec I would guess 260hp.
 

BigChris

Seaman Apprentice
Joined
Apr 25, 2016
Messages
39
I would expect with a towing cam (from the RV), 8.5:1 compression ratio, vortec heads, reasonable dual plane intake manifold, and properly jetted 4 barrel carb you should achieve about .8 hp per cubic inch. That should get you in the 280ish hp range.

For more, two things that come to mind are higher compression ratio, and more cam.
 
Joined
May 27, 2016
Messages
18
Still haven't seen the motor and I'm a little confused and interested in this motor. So it's an early 80's rv he bought a new 350 sbc short block about 10 yrs ago and bolted on the alt, pwr str etc. What i don't know is if he put the old heads on a what kinda block he bought. Gonna be interesting ordering the gaskets and such...if this all pans out
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
40,581
Still haven't seen the motor and I'm a little confused and interested in this motor. So it's an early 80's rv he bought a new 350 sbc short block about 10 yrs ago and bolted on the alt, pwr str etc. What i don't know is if he put the old heads on a what kinda block he bought. Gonna be interesting ordering the gaskets and such...if this all pans out

You know he might have bought the same vintage motor in 1993. More or less replaced with same motor he had

Would need to check casting numbers
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,465
So it's an early 80's rv he bought a new 350 sbc short block about 10 yrs ago and bolted on the alt, pwr str etc. What i don't know is if he put the old heads on a what kinda block he bought.

Ayuh,.... Welcome Aboard,.... Like Scott says, the castin' numbers will tell ya what you've got to work with,.....

The head's numbers are on top of the heads, under the valve covers,....

The block's are portside aft on the top of the block flange,....
 
Joined
May 27, 2016
Messages
18
Yeah so he bought a short block from GM in 2005-06. Haven't got the #'s yet but i will to up date. Its a 1985 coachman rv. So he bought a new block and heads truck motor and bolted everything else from the old motor back on. ...he's got a 4 barrel carb on there couldn't tell which kind. I'll kno more with the #'s. Hopefully you guys can help me with the headgaskets and such
 

flipbro

Master Chief Petty Officer
Joined
Feb 8, 2013
Messages
830
good stock replacment. 4 bolt main. Built in mexico.IF thats what it is
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,465
Date: 1995-1999
Notes: 350, 4 bolt, crate engines and ZZ4, roller cam, one piece rear seal

Ayuh,.... That's what ya got,....
 
Joined
May 27, 2016
Messages
18
Yes, I did look that up. How close is that to what i had? I do need to change head gaskets and a bunch other stuff lol. Has a rochester quadrajet as well as my boat did. 14057055 air intake
 
Top