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engine change from mercruiser 120 to 4.3 liter - need help on exhaust change fix

mdy2273

New member
I had a 120 mercruiser and bought a 4.3 engine for more power. The 120 engine manifold was a single exhaust on the left side and the new exhaust on the 4.3 is a dual and has a exhaust point in the center. Is there a fix for this?
 
I f the 4.3 is same vintage as the 120 coming out - you just unbolt the single, and bolt in the Y pipe. there's no fix needed.
the 120 might have the manifold on the left side, but the exhaust doesn't exit the boat on the left - it exits dead center as it does on all mercruisers

If you don't have the proper Y pipe- i.e. yours doesn't line up....you need to buy a Y-pipe like this
320_MERCRUISER-MERCURY-STERNDRIVE-EXHAUST-Y-PIPE_310268646707_0.jpg
that is proper for the year of your transom assembly..i.e. look in the parts listings for a V6 or Chev V8 the same year as your 120
 
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yes to the above.

Also you need to have stringers in the right places to mount the 4.3.

Then you need new gearing in the drive.

The wiring harness might be the same. If the new motor is close in year to the old one.

Just leave every wire in place and remove from the motor what you have to remove.

What i think might happen is you will have to lenghthen some wire.

The flywheel and coupler, might be ok ?

What i am trying to remember if the 120 coupler will fit the 4.3?

What coupler you have on it now ? A one piece triangle, or rubber one ?

Maybe someone else will chime in.
 
Gonna need a different prop too, most likely. Better to look for a complete drive out of a boat with a 4.3
 
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