Swap a complete 1988 OMC 4.3 out and put a complete 5.7 Mercruiser I/0 complete with wiring harness in??

MFIC1960

Cadet
Joined
Jun 13, 2022
Messages
10
1988 OMC 4.3 remove and replace with a 1991 5.7 mercruiser
Will there be any issues with transom cut out or anything else.

Thank you
 

nola mike

Vice Admiral
Joined
Apr 22, 2009
Messages
5,664
Same width, you'll need some extra room up front. Motor mount locations are different. Cut out is the same. You'll need a *complete* engine package, controls, wiring, exhaust, etc.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
51,146
make sure there is 4" extra up front.

motor mounts will be 4" forward

cut out is similar, most you will need to do is a bit of clearance for the tiller arm.

as Mike stated, pulleys to prop, with controls and wiring

when you pull the engine out of your 1988 boat, check the stringers and transom for rot. do a few test drills
 

MFIC1960

Cadet
Joined
Jun 13, 2022
Messages
10
Yes Sir ! I have the complete wiring, throttle/ steering and all wires down to the fuse and horn. Lol🤪
I appreciate your input. My local boat shop was telling me it’s not the same cutout on the transom.
And all stringer's and transom are solid. It actually a 1988 Playcraft 24’ hard top pontoon. So plenty of room 😄
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
51,146
Make sure the center pod is firmly attached
 

nola mike

Vice Admiral
Joined
Apr 22, 2009
Messages
5,664
Yes Sir ! I have the complete wiring, throttle/ steering and all wires down to the fuse and horn. Lol🤪
I appreciate your input. My local boat shop was telling me it’s not the same cutout on the transom.
And all stringer's and transom are solid. It actually a 1988 Playcraft 24’ hard top pontoon. So plenty of room 😄
V8 seems a bit of overkill in a toon, no?
 

MFIC1960

Cadet
Joined
Jun 13, 2022
Messages
10
Make sure the center pod is firmly attached
It’s all in nice condition, even the original seats. I had a 22’ Wellcraft. I had a semi built 5.7 built probably 340 to 390 HP.
Be for the motor when in we a nasty snow storm and about 25 trees down including
A monster that took out that boat.
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
.... My local boat shop was telling me it’s not the same cutout on the transom....
That's an OMC Cobra, and if the cutout isn't the same, it's VERY close. All you might need to do is drill a coupe of 11mm holes at the top of the cutout.
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
It’s already 30 MPH, after we make and install stakes and motor it should be a 45 mph minimum!!
Just a fun toy, pretty much a sleeper.
I think you're being a bit optimistic. If it's making 26knots with the V6, I think you'll only make about 5 or 6 knots more with a V8. Power vs speed increase is NOT linear, it follows the rule of squares. ie, doubling the power does not double the speed, it'll only increase it by about 15% to 20%.

Chris......
 

MFIC1960

Cadet
Joined
Jun 13, 2022
Messages
10
I think you're being a bit optimistic. If it's making 26knots with the V6, I think you'll only make about 5 or 6 knots more with a V8. Power vs speed increase is NOT linear, it follows the rule of squares. ie, doubling the power does not double the speed, it'll only increase it by about 15% to 20%.

Chris......
Okay, will sends pics later….
 

MFIC1960

Cadet
Joined
Jun 13, 2022
Messages
10
Same width, you'll need some extra room up front. Motor mount locations are different. Cut out is the same. You'll need a *complete* engine package, controls, wiring, exhaust, etc.
Just found this?? Maybe the opening is not the same???
 

Attachments

  • 8FB278E7-C03C-435A-871F-9FAB7F51C2C2.jpeg
    8FB278E7-C03C-435A-871F-9FAB7F51C2C2.jpeg
    38 KB · Views: 5

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
51,146
you will not need the AQ to SX conversion.

you simply need to unbolt the OMC, bolt in the mercruiser.
 
Top