Swap 4.3 for 3.0L Mercruiser

[Tyler Shurigar]

I am looking at purchasing a 02 Bayliner with a 3.0L Mercruiser that has a cracked block. Has anyone ever replaced the standard 3.0 with a 4.3L I know that it was a factory option on this model - I understand the difference between the straight 4 and V6 - but am curious as to what all would have to be changed - would the 4.3 bolt right up to the lower unit or would an adaptor have to be used?<br /><br />Any input would be appreciated

 

[Haut Medoc]

Re: Swap 4.3 for 3.0L Mercruiser

Welcome to iboats You would need new motor mounts for sure & I doubt if your drive's gear ratio would work with a 4.3......I'm sure you'll get more feedback.....Sit tight!......JK

 

[pgorske]

Re: Swap 4.3 for 3.0L Mercruiser

I'm about to do the same thing. I have searched and many people say it's not worth it. Too much to change. My case I think is different. I have a donor boat so I will be using everything including transom plates power steering etc. I will be using my 3.0 lower unit. As I understand it the ratio for the i4 is 2.0 and for the v6 it's 1.8. How big of deal is that? Would guess that I would have more out of the hole pull?? What performance impact will the .2 make? Also will need to match up wiring. Will that be difficult?<br /><br />thanks

 

[whywhyzed]

Re: Swap 4.3 for 3.0L Mercruiser

TBolt has the best situation with the complete donor boat. If you can find a wrecked/neglected boat always best.<br />The ratio may be corrected by changing props to a higher pitch. <br />Now, I don't know why.... but having corrected ratios before with prop changes it never seems to be 100% right even when you get the end speeds and rpm's right. <br />Something to do with torque/rpm (and thus HP) relationship happening at a different place (in the water as opposed to in the verticle drive) seems to make less efficient..

 

[Haut Medoc]

Re: Swap 4.3 for 3.0L Mercruiser

Tbolt.....Your engine will not achieve full W.O.T. with that gear ratio & will most likely 'Lug' which will cause all kinds of bad things, ie. piston failure......1:98 as opposed to 1:84 is significant when you only have a six cylinder.......JK

 

[JJJ]

Re: Swap 4.3 for 3.0L Mercruiser

JK I think you have it backwards. He will have more torque. May not achieve the same speed but out of the hole should be awesome, just needs the right prop.

 

[pgorske]

Re: Swap 4.3 for 3.0L Mercruiser

JK, I never have been that great with the whole ratio thing, but I just don't understand. If a 130hp 4 cyl motor can achieve WOT with a specific gear and prop, how is it possible that a 190hp v6 would not be able to as well?

 

[whywhyzed]

Re: Swap 4.3 for 3.0L Mercruiser

JJJ is right, that's backwards and this is getting confusing, but the 6 cylinder will over-rev with the 4 cyl outdrive ratio, not lug. a new prop will then bring the revs down, the mph up, green of envy to your friends, chicks to your slip etc...

 

[whywhyzed]

Re: Swap 4.3 for 3.0L Mercruiser

double posted sorry

 

[tommays]

Re: Swap 4.3 for 3.0L Mercruiser

your more likely to need a 1.65 ratio to take full advantage of the power of the 4.3 on a small boat<br /><br /> this boat could have allready used a 21 in prop with the 3.0 the extra 60 to 80 HP of the 4.3 with a 2:1 ratio would need a REALLY BIG PROP <br /><br />it would work but it does not seem to work well with out the correct ratio for the motor<br /><br />tommays