5.7 350 year question

[Bigfoot0220]

I have a seized 4.3 that I am looking to swap out for a 5.7. I have been doing a lot of research, and am confident that it can be done in this boat. It is a 1995 Trophy 2359, Aplha Gen II. It was originally offered with a 5.7 and there's plenty of room. I know I will need to move the front mounts. I know the gears will need to change. My question is, I am seeing a lot of engines out there listed as 1997 and up, or similar. What I can't seem to decipher is why any of these wouldn't work as a drop in since it would be a complete motor. Is there something I'm missing?

For instance, I am considering this 5.7 from Rapido https://www.rapidomarine.com/default.aspx?p=/complete_engines.aspx

I'd need to get new exhaust manifolds and risers, but the rest of the components should be compatible from my current 4.3, right? If the new motor has the same 10 pin engine harness, it should be ok? I have an electric fuel pump, so that system should be ok. currently have Thunderbolt IV ignition, and I'm not sure of any impact with getting an engine with a different system.

Any help would be greatly appreciated.

 

[QBhoy]

Depending on the ratio you have now...you likely get away with just going up a bit in pitch with prop instead of a ratio change.

 

[alldodge]

Unless you stick with per-vortec then some of your stuff will not fit a vortec motor. The intake is different, and many cases the bosses to mount the power steering and alternator is different

 

[Bigfoot0220]

Depending on the ratio you have now...you likely get away with just going up a bit in pitch with prop instead of a ratio change.

I'm planning on trying that, but am prepared to replace upper and lower units if necessary. I'm at 1.84 now, which seems like it should work as its the high altitude ratio for the 5.7. I'll try it and see first.

 

[Bigfoot0220]

Unless you stick with per-vortec then some of your stuff will not fit a vortec motor. The intake is different, and many cases the bosses to mount the power steering and alternator is different

So, I believe the 4.3 in it now is the Vortec. Or at least it has Vortec branded valve covers. I'm also looking at the 5.7 357 Mag Alpha complete motor. I like the idea of dropping in a complete, and wouldn't have to worry about compatible parts as much, and I can sell off parts from the old motor.

If I did do this one,
https://www.michiganmotorz.com/comp...gnum-alpha-mercruiser-applications-p-892.html do you know if I can easily convert from mechanical to electric fuel pump? And is there any reason I can't swap over the closed cooling system from the 4.3?

Thanks

 

[QBhoy]

So, I believe the 4.3 in it now is the Vortec. Or at least it has Vortec branded valve covers. I'm also looking at the 5.7 357 Mag Alpha complete motor. I like the idea of dropping in a complete, and wouldn't have to worry about compatible parts as much, and I can sell off parts from the old motor.

If I did do this one,
https://www.michiganmotorz.com/comp...gnum-alpha-mercruiser-applications-p-892.html do you know if I can easily convert from mechanical to electric fuel pump? And is there any reason I can't swap over the closed cooling system from the 4.3?

Thanks

If you drop in a 350 mag mpi you’ll defo need to change the ratio. Haha.

 

[alldodge]

For the most part drop in and go. If you get a complete drop in, then it comes with electric fuel pump. Changing to an electric is easy enough.

You will need to move the front motor mounts a bit

 

[Scott Danforth]

I have a seized 4.3 that I am looking to swap out for a 5.7. I have been doing a lot of research, and am confident that it can be done in this boat. It is a 1995 Trophy 2359, Aplha Gen II. It was originally offered with a 5.7 and there's plenty of room. I know I will need to move the front mounts. I know the gears will need to change. My question is, I am seeing a lot of engines out there listed as 1997 and up, or similar. What I can't seem to decipher is why any of these wouldn't work as a drop in since it would be a complete motor. Is there something I'm missing?

For instance, I am considering this 5.7 from Rapido https://www.rapidomarine.com/default.aspx?p=/complete_engines.aspx

I'd need to get new exhaust manifolds and risers, but the rest of the components should be compatible from my current 4.3, right? If the new motor has the same 10 pin engine harness, it should be ok? I have an electric fuel pump, so that system should be ok. currently have Thunderbolt IV ignition, and I'm not sure of any impact with getting an engine with a different system.

Any help would be greatly appreciated.

your motor is a 95. it may have vortec on the valve covers, however it is not a vortec headed motor

vortec headed motors came out in 96 regardless of what marketing hype was on the valve covers starting in the late 90s its a case where a name was used 8 years prior to the technology coming out.

if you pull a 4.3 to drop in a 5.7..... throw away everything 4.3 and buy a complete bob-tail 5.7 is the easiest/least costly method

your ignition from a V6 wont work with a V8
some of your accessory drive parts from the V6 will work, however not all

your alternator and starter will work
the basic wiring harness can be made to work, however you may need to lengthen 3 or 4 wires
your flywheel would be the same, therefore the coupler would work, however i believe the V8 couplers have a thicker drive plate
you may be able to use the mount brackets

then there is the gear ratio. if you have a 1.62:1 drive, you may be able to prop enough. if you have the 1.84:1, you need new gears.

the closed cooling of a 4.3 would not have enough capacity for a V8