470 conversion to 4.3

[mr 88]

Ready to buy boat that has a 470 with low compression in #3 136-130-105-135. I can buy a running 1988 470 with good compression for 500.00 or pick up a hull with a 4.3 drive line for 12-1500...Will the 4.3 fit in the engine compartment would be my first question.Are the depths of the engine comparable as in will I be resting on the oil pan with the 4.3 Then are the mounts compatible,been told the sterns are the same but I would have to fabricate the front bracket. Are the controls and gauges interchangeable as in plug and go or will I be splicing.I want to be able to troll and from what I can remember the 4 cylinders are a bit lumpy compared to the 6s and that is why I am thinking about the 4.3...Any recommendations one way or another are welcome............

 

[matt167]

Re: 470 conversion to 4.3

Harnesses will work if you go same year to same year or within the range. 1983 and earlier 470's need a full swap to use a 4.3L, but 1984-1989, you need the coupler, manifolds and the Y pipe for the 4.3 and it will fit the transom plate. Probably need to rework the stringers. Drive ratio in the LU is also right. Some engine compartments are narrow, but many are big enough to fit V8's which were often optional and thus the 4.3L would fit right in.

 

[HT32BSX115]

Re: 470 conversion to 4.3

Will the 4.3 fit in the engine compartment would be my first question.

More than likely YES. But since you didn't reveal dimensions in the boat, I would do a little measuring. MOST manufacturers designed their boats to be offered with several of the optional engines offered in the day.....

Are the depths of the engine comparable as in will I be resting on the oil pan with the 4.3 Then are the mounts compatible,been told the sterns are the same but I would have to fabricate the front bracket.

If there are no "SIDE" mounts that most V-6/8 engines require, you'll have to fab them and if they're there, you may have to move them.

Are the controls and gauges interchangeable as in plug and go or will I be splicing.I want to be able to troll and from what I can remember the 4 cylinders are a bit lumpy compared to the 6s and that is why I am thinking about the 4.3...Any recommendations one way or another are welcome............

Yes. Mercury's "10 pin" engine plug is pretty much "standard". There may be additional pins/wires in the harness for oil-press, temp alarms, in newer engine harnesses etc.

The harness in the "donor' boat might be in better shape than your current one so you might want to swap it.

I actually could have used the harness and plug from my previously installed OMG 460 King Kobra but the (454/Bravo) Mercury harness had 2 additional pins (12 total I think, but it was the "same" plug) and wires for the alarm circuit and something else (can't remember)

But more important, the Mercruiser harness was in PRISTINE condx! (and longer since it came out of a larger boat) So I was able to rewire everything using new clean marine crimp connectors etc.

You'll like the 4.3L engine. Like the older 165 L6, it's one of the best engines ever offered in a boat! and it uses the same ratio drive as a 3.7L

 

[mr 88]

Re: 470 conversion to 4.3

Harnesses will work if you go same year to same year or within the range. 1983 and earlier 470's need a full swap to use a 4.3L, but 1984-1989, you need the coupler, manifolds and the Y pipe for the 4.3 and it will fit the transom plate. Probably need to rework the stringers".

The 470 is a 79 and the donor 4.3 probably 80 to late 80's. So if I pull everything out but the transom plate a complete 4.3 should be ready to bolt in after front mount brackets are made. It will be cheaper to buy a complete older boat then a engine by it self so I will have all the items you mentioned,correct ?

 

[matt167]

Re: 470 conversion to 4.3

Inner transom plate will be wrong for a '79 470- 4.3L. You will need a transom plate also... If there is a possibility of using your MC1 leg ( it's the right ratio ), it would be done by using an Alpha transom assembly with your MC1 leg, which should work because they can be put together the other way round ( Alpha leg on an MC1 ), but I'm not sure if they really were forwards compatible... Unless the aftermarket makes a conversion coupler. The crank bolt pattern changed for 1987 leaving only about 1 year ( 1986 ) of 4.3L's compatible with the old setup, unless I'm mistaken..
A 1985-1986 Chevy Astro long block would be the only other application I think

Edit. To make this a sure fire way, get a Mercruiser 305 from 1986 or earlier. You can swap the transom plate and run your 470 leg, and the ratio will still be ok for the 305.

 

[stonyloam]

Re: 470 conversion to 4.3

Swap the 470's part out the old one, should almost break even. Waaaaay less PITA factor, have a running boat in a weekend. IMHO, but then I'm a "470 guy".

 

[Fun Times]

Re: 470 conversion to 4.3

Ready to buy boat that has a 470 with low compression in #3 136-130-105-135. I can buy a running 1988 470 with good compression for 500.00 or pick up a hull with a 4.3 drive line for 12-1500.

Hi there mr 88, Just dropping in to let you know that I had moved your thread to the proper location to follow forum guidelines due to your thread did not appear to be an engine repair and maintenance type discussion but rather an non-repair discussions not involving troubles or repair.

Apologies for the inconvenience, Hope your project goes well for you, Good luck.