4.3 or 5.7

[john200]

I just bought a boat that has a "bad Motor" so I was told when I bought it so my question is do I replace the 4.3 with a new vortec 4.3 and yes I know that I will have to do a few mods to switch to the vortec new intake and cam and 4brl carb that's fine. I know what I will need for this swap but what will fit the 350 off the 4.3 and what will I need to get to swap in the 350 that I don't have just looking at cost and power I know that the parts for the 4.3 vortec will run 600 or so so to those of you that have swapped out for the 350 what did it take parts wise

 

[ryendube]

Re: 4.3 or 5.7

I just bought a boat that has a "bad Motor" so I was told when I bought it so my question is do I replace the 4.3 with a new vortec 4.3 and yes I know that I will have to do a few mods to switch to the vortec new intake and cam and 4brl carb that's fine. I know what I will need for this swap but what will fit the 350 off the 4.3 and what will I need to get to swap in the 350 that I don't have just looking at cost and power I know that the parts for the 4.3 vortec will run 600 or so so to those of you that have swapped out for the 350 what did it take parts wise

well you would be buying complete long blocks with intake and carb weither its a vortec 4.3 or 5.7 but added cost of the manifolds. pretty sure all accessories swap over

 

[Bondo]

Re: 4.3 or 5.7

Ayuh,... The 5.7l would require regearing the outdrive as well,... Add another $1300. for that...

 

[wca_tim]

Re: 4.3 or 5.7

depending on what kind of a boat it is, you can probably get by with the current gear ratio and reprop. I was asking the same question a year or so ago and the machinist / engine builder I used told me not to change gear ratios until I had a chance to run it. He was spot on.

If you do decide you need to change, and your current drive is in decent shape, just buy a new upper half which is more like 600 - 700. That's what determines the gear ratio.

Depending on what you're like... I did the v6 route first, decided I wanted more and so put a v8 in it...

respectfully submitted...

 

[mylesm260]

Re: 4.3 or 5.7

and yes I know that I will have to do a few mods to switch to the vortec new intake and cam and 4brl carb that's fine.

4.3 vortecs (1996 and newer) run the same cam in the truck version as the marine version.

Only thing you would need to change would be the intake manifold, and the head gaskets, unless you're running a heat exchanger.

 

[john200]

Re: 4.3 or 5.7

so to start off withe the 5.7 I would need to get intake and exhaust manifolds carb what about motor mounts are they the same do I have to make any hull mods

 

[mylesm260]

Re: 4.3 or 5.7

Same physical mounts, just a slightly different offset, I believe. 95% chance you won't have to make any mods.


What prop pitch are you running right now?

 

[Maclin]

Re: 4.3 or 5.7

I would have to ask more about what "bad motor" means. Was the boat running last year but now has a cracked block from a failed winterization? or was it submerged for 2 years and brought back to the surface and sat another 2 years? Little pieces of info like that make a big difference in what advice I would give.

I would take the engine apart and inspect it all. If just a cracked block I would tend to replace/marinize the block and re-furb the heads, get new exhaust manifolds and head to the lake.

If you want it to be a total loss to justify an upgrade then that is a different situation. There has been a recent thread here about a very successful vortec and 4bbl upgrade to a 4.3. It would be good reading for someone wanting to upgrade a busted 4.3

 

[mylesm260]

Re: 4.3 or 5.7

agreed...

a vortec 4.3 is a huge upgrade over a non vortec 4.3

I had to go from a 19P 3 blade prop to a 23P 4 blade prop, and my WOT rpms are STILL higher than before.

If you're exhaust manifolds are good, I would say get yourself a used truck motor (4.3) 2001 or newer if possible and a new intake manifold and a 4 bbl carb (if you don'y already have one)

If you don't have a heat exchanger, now would be a great time to install one, otherwise, you will have to change the head gaskets and the water pump on the truck vortec.

You may also run into a flywheel and starter issue, depending on what sized flywheel you're running, as well as a V-belt to serpentine issue with you're power steering and alternator. The truck power steering pump is working well for me, I just had to source a later generation marine alternator that was serpentine.

good luck!

 

[john200]

Re: 4.3 or 5.7

well I don't know much about this boat but when I got it home I looked at the motor and it must have froze because the head is torn split and so is the manifold so it looks like I will have to get thous to so more and more its looking like a 350 chevy is in the near future and as far as the prop it looks to be a 23inch so now I am looking for manifolds for a 305/350

 

[wca_tim]

Re: 4.3 or 5.7

if you get a chance... imco, emi or stainless marine.

mounts move forward a little over 3 inches and you'll need over 4 inches more space in the front to accomodate the longer engine.

a nicely set up vortec v-6 is also a great option. a vortec 350 is another big step up from there. I liked the 4.3 in mine, but it topped out shy of 60 and just didn't have the power I really wanted, so I went with a small
block...

All depends on what you really want and how much you want to spend...

 

[mylesm260]

Re: 4.3 or 5.7

well I don't know much about this boat but when I got it home I looked at the motor and it must have froze because the head is torn split and so is the manifold so it looks like I will have to get thous to so more and more its looking like a 350 chevy is in the near future and as far as the prop it looks to be a 23inch so now I am looking for manifolds for a 305/350

If you've got a 23 pitch with you're existing 4.3, then bondo is absolutely right....

going to a 350 would require new upper gears......