3.0 OMC (gm) to mercruiser 4.3 swap

[Berger Heating]

Hello all,

I have decided to bite the bullet and replace the motor in my boat

Here are some introductory details- it is a 1988 crestliner phantom 185 - aluminum bowirder - 2080 dry weight
It came from factory with a 3.0 Omc, cobra drive gm block -

I recently have been working with a friend of mine that works at a marina - he has a 4.3 mercruiser, that we plan to dress with Omc exhaust manifold, new y pipe and bell housing from an omc 4.3

We have heard both stories about changing gear ratio for the larger engine, or just re propping the current drive

Any input on swaps done would be helpful. And based on the weight of the boat plus new engine, what prop size ? 19 pitch ? 21 ?

Thanks !

Alex

 

[Bondo]

he has a 4.3 mercruiser, that we plan to dress with Omc exhaust manifold, new y pipe and bell housing from an omc 4.3

Ayuh,..... Welcome Aboard,..... Are these the ole one piece manifold/ riser units, aka: bat-wing manifolds,..??..??

If so,... Don't do it,.... They were Junk the day they were new,.....
Core-shift caused many to mostly Bad castin's that leak water into the motor, killin' it catastrophically,...

As for propin' it,....

I tried runnin' a 3.0l outdrive on my Merc 4.3LX, 'n with a 26" prop, it over-reved, Alot,...
4800 rpms was extremely slow,... 30-something, insteada 40-something with the right gear ratio, 'n a 19" prop,...