merc v6 to v8 swap

[chartersj]

I recently bought a project boat, a 1993 bayliner 2052 which needs a new motor. The 4.3 that is currently in the boat had rain water fill the motor and froze in the winter about 4-5 years ago, then was drained but left untouched after that exposed to the elements until now. Its seized, the frost plugs are pushed out and has a cracked manifold, also all I get it rusty water when I pull the dip stick. So rather than tear it completely down and rebuild it I am looking for a whole new motor. I have been reading on v8 conversions and it seems quite simple to do. As far as I can tell just move motor mounts 4.4", exhaust work and re-gear or add a larger prop to compensate for the more hp. Are far as the electrical side, to make it work do I need to find a 5.0 or 5.7 with thunderbolt ignition from year 92 to 94? or will any year with thunderbolt IV work?

 

[alldodge]

You have it pretty well in hand so far as what to do to mounts, exhaust, ratio or prop.

Any TB-4 or 5 will work so long as its for a V8, only the module is different. Could also go with Delco EST

 

[Fishermark]

...Could also go with Delco EST

That would be what I would recommend if your situation. If you show around you can get a good deal on a complete set up.

 

[Fishermark]

You can buy the complete set pictured below here for only $239.

 

[Rick Stephens]

Your boat electrical system won't care what motor or distributor you choose. As long as it is marine rated you'll be golden.

More motor sounds good. Complete units are spendy but give you everything in a drop in package

 

[alldodge]

One thing to note before you drop in more power, make sure the motor doesn't exceed the max HP listed on the USCG tag.

 

[Alumarine]

If you're going to do all that work I'd go for the 5.7 over the 5.0.
Same price and weight. Lot's more oomph.

 

[chartersj]

There is a tag on the back of the transom that says not to exceed 205hp. I find it hard to believe that it wouldnt be just as reliable with a 5.7 mounted to it. Would be be due to the thickness of the transom compaired to other models?

 

[thumpar]

It has to do with the rating the USCG gives it. I think there is a formula they use. The transom thickness is the same. You could easily find a 4.3l motor out of a truck or van to replace what you have. You just need to replace the core plugs and swap your externals over. I wouldn't go over the rating for insurance reasons.

 

[Rick Stephens]

Not worth it going to a v8 with that limitation. Easy to push a v6 to over 230 hp. Less weight will keep the boat snappy.

 

[tank1949]

I am looking at a couple of older Sea Ray Amberjacks. One has (2) 4.3 at 205 HP each, but boat's dry weight is 6500 + lbs. I am sure 5.7 will get it close to 50 mph, WOT. I had an 86 with 5.7s and it would fly. I suspect the 4.3s would push it about 42 WOT and cruise at about 23 -26 mph while under 3000 rpms. I also suspect the 4.3 would not suck as much fuel. My 5.7s burned about 10 gals and hr each if I ran it under 3000 rps. It calculated close to running 30 miles for 20 gals. I am curious if anyone has compared the 4.3s?

 

[chartersj]

It has to do with the rating the USCG gives it. I think there is a formula they use. The transom thickness is the same. You could easily find a 4.3l motor out of a truck or van to replace what you have. You just need to replace the core plugs and swap your externals over. I wouldn't go over the rating for insurance reasons.

Do you know what year range for automotive 4.3 engines i should be looking for? I think this may be my best option

 

[Scott06]

You might also check the fuel pump. Most likely the original '93 engine had a mechanical fuel pump, if you get a newer block regardless of if its a 4.3 or 5.0/5.7 it will not accept a mechanical fuel pump. You can buy a complete kit with pump and hose, but will need to wire it through an oil pressure switch and starter solenoid. I've seen a few posts on this or maybe someone more experienced than me can all you through it.

 

[chartersj]

You might also check the fuel pump. Most likely the original '93 engine had a mechanical fuel pump, if you get a newer block regardless of if its a 4.3 or 5.0/5.7 it will not accept a mechanical fuel pump. You can buy a complete kit with pump and hose, but will need to wire it through an oil pressure switch and starter solenoid. I've seen a few posts on this or maybe someone more experienced than me can all you through it.

Thanks, I just looked into this and from the information I could find the last year merc used mechanical fuel pumps was in 1992. I am going to take a closer look today to see if it does or not but i'm thinking it does not. So if that is the case will any 4.3 from 1993+ work? I know of a 2005 4.3 engine out of a blazer with 140000 kms on it that seems like a good donor if its the right block

 

[alldodge]

I would suggest getting a newer motor which will have vortec heads and thereby increasing HP. Then just add the electric fuel pump and go

 

[chartersj]

Well I think mine has a electric fuel pump already, I was talking with a mechanic and he was saying the valves in the heads are made of different material in an auto motor verses a marine. Any truth to that?

 

[alldodge]

Well I think mine has a electric fuel pump already, I was talking with a mechanic and he was saying the valves in the heads are made of different material in an auto motor verses a marine. Any truth to that?

No such thing.
Difference between a truck motor and a marine one is the marine uses brass core plugs (freeze plugs), stainless head gasket and marine circulating water pump (brass insides).

 

[chartersj]

No such thing.
Difference between a truck motor and a marine one is the marine uses brass core plugs (freeze plugs), stainless head gasket and marine circulating water pump (brass insides).

OK thanks a lot for the info!. So other than changing the freeze plugs, head gaskets, and water pump, I would have to look for a 8 bolt intake manifold for a 4-barrel carb? Would my carburetor have to be adjusted for the small increase in hp? Anything else other than swapping over the marine accessories?

 

[Rick Stephens]

Your carburetor would probably have to be adjusted. I just went through that with a new carb, the factory non-Vortec jetting was too lean by a goodly margin. Vortec motors breath better, hence more HP and different airflows through the carb, necessitating the jet changes.

 

[alldodge]

If your running in fresh water and find a truck motor in the junk yard, you can get away without changing the head gasket IMO, others may say different.

Ricks got the rest covered

As for swapping accessories, you should be good