4.3L Merc swap to Merc V8

[mankorn427]

I want to know if anybody has done a similar swap on a boat about 20ft or so... I want to swap my 4.3L V6 carb Merc out for something like a 5.7 or an offshore 355 Merc w/ Bravo 1 outdrive. I am very serious about doing a swap like this in my boat. I have the space and weight capacity in my boat available to allow this swap. I am looking for tips on this swap. Like what can I do to relocate the mounts on the boat for the engine, will a Bravo 1 drive fit in place of an Alpha, is wiring going to be a pain to go from carb to EFI, would thru hull exhaust going to be hard to cut in and plumb, etc...? Thanks

[Beech2000]

Sorry folks but I feel compelled to answering this even though thread is almost a month old.

ARE YOU NUTS?

Sorry but it was my obligation!

Not a practical swap. If the V6 Alpha runs good then sell it for a speed boat with Bravo drive installed from factory. You'll save huge amounts of time and have a more suitable combination. Besides how fast do want to go? V6 20ft. boat should already be able to go 45-50+. Anything more than that in 20ft is uncomfortable.

If above went in and out of ears like it would me then hear are some immediate differences

Alpha's have fresh water pump in lower unit which pumps lake or ocean water up to engine. Bravo drive has a seawater belt driven accessory.

Mounting differences between the units are many. Nothing is interchangeable between the two except the mercruiser decals for which you may want to seriously consider. You will need to have complete bravo drive complete with transom mount. Bell and gimble housing, gimble ring etc...

I take it you haven't purchased an engine yet but do want to offer an option that will work provided you limit hole shots and that is to simply drop in your favorite 5.7 liter engine in place of the V6 and run the Alpha Drive with 1.50 if Alpha gen one or 1.47 with gen two. You will still need a complete engine with all brackets, accessories, wiring harness electric fuel pump etc... If engine is complete pull out from running boat than you should be all set regardless if carb or EFI. Minor wiring changes if late model boat. Any way as long as you limit hole shots and keep engine horse power below 300 than the Alpha will hold up fine. *Stock V6 gear ratio should be around 1.62 and will not hold up with higher power V8's. Gear ratio can be determined in Alpha units by counting teeth in gears. 20/22 is the preferable 1.50/1.47. More teeth =higher gear ratio and change out required.

I'm done.

[steele m.a.]

I agree . Perhaps you can help me with a similar , but saner swap.
We've a 20 Campion minus engine , we bought it with a 188 hp Bravo
on a bare hull. We also purchased an old fiberform 19 , with a 6 cyl
merc in very good shape , but bolted to a very old Alpha , which is
badly corroded. The owner of this project boat (boats) asked me if I could
install the 6 in the Campion , and somehow mate it to the Bravo. I told
him I could put the engine in , and build all the neccesary fuel and
cooling systems , but that I didn't know what his chances were at mating
a 240 6 onto a Bravo outdrive , can you help ?
markalfredsteele@yahoo.ca

[Beech2000]

I agree . Perhaps you can help me with a similar , but saner swap.
We've a 20 Campion minus engine , we bought it with a 188 hp Bravo
on a bare hull. We also purchased an old fiberform 19 , with a 6 cyl
merc in very good shape , but bolted to a very old Alpha , which is
badly corroded. The owner of this project boat (boats) asked me if I could
install the 6 in the Campion , and somehow mate it to the Bravo. I told
him I could put the engine in , and build all the neccesary fuel and
cooling systems , but that I didn't know what his chances were at mating
a 240 6 onto a Bravo outdrive , can you help ?
markalfredsteele@yahoo.ca

Distinguishing feature for engine mounting is dictated by the flywheel housing for particular engine for either Alpha or Bravo.

Transom plates are same for Bravo line but obviously different than the Alpha but so as long as you have the complete flywheel housing assembly for the 240hp you should be fine. I think. LOL

188 HP was a Diesel right?

[steele m.a.]

No - the 188 was a 302 Ford.The Fiberform is rated as a 155 with the
6 cyl (Ford) on it.