I Need 4.3/5.0 Swap Tips

G

GJarrett

Member
Oct 3, 2006
649
Tampa, FL
Boat Info
'02 260 Sundancer
Engines
6.2 MPI
I found a 5.0LX at Lake Lanier GA in very good condition for a screamin' good price so I'm going to pick it up tomorrow.

I'll be replacing a carbed Thunderbolt ignition 4.3LX with a carbed Thundderbolt ignition 5.0. I've been told by those who are supposed to know their stuff that this should be an easy drop-in swap; I won't even need to change motor mounts. Is this true, or am I going to get surprized midway through the swap?

All tips and tricks are appreciated. Right now my biggest concern is where to find a motor hoist that is high enough to clear the boat and trailer since a standard auto engine hoist is about 6 ft too short :smt017
 
Call Hall Marine in Greenville and talk to the Service Manager. They can probably answer all your questions including where to rent a lift.

I would think you will need some parts especially when it comes time to hook up your throttle and shift cables as well as your exhaust tubing. Does it come with a coupler too and if so will that fit the splines of your alpha drive? What about manifolds risers and elbows?
 
I'm learning a LOT today and have now gotten even more options. I'm still going to drive to Georgia to go look at that 5.0; however.....

.....the 4.3LX I have with the 4 bbl carb has almost the same hp as the much heavier 5.0 V8 and now I've found a local marine shop that can rebuild the 4.3 I have for a LOT less than any of the engines I've been looking at, put a torque cam in it to give it more umph getting up to plane, and offer a 3 yr warranty (!) [the engines I'm looking at are used with unknown hours]. That's gonna be hard to turn down, though I've been salivating for a biggun V8 in Offroad Dancer. If I can rebuild what I already have with better low-end torque I'm not too sure how much less performance I will notice coming up to plane with that cammed 4.3LX 205hp engine compared to a 5.0 220 hp engine that weighs about a hundred and fifty pounds more (and won't be warrantied). :smt017

I probably won't know what I'm gonna do until the minute I do it.... this is a very difficult decision for me.
 
It's your money but if I could have my engine rebuilt and get a three year warranty and spend less money...............I think I would choose that option.

If you get in over your head with a used V-8 you could wind up spending a lot of bucks beyond the initial cost of the engine.
 
Dave S said:
It's your money but if I could have my engine rebuilt and get a three year warranty and spend less money...............I think I would choose that option.

If you get in over your head with a used V-8 you could wind up spending a lot of bucks beyond the initial cost of the engine.
Click to expand...

Big Ditto :thumbsup: :thumbsup:
Keep us informed on how it goes. Hope you get back on the water soon :thumbsup:
 
Research is the key here. Who would be rebuilding the 4.3? Are they a MARINE performance shop? If not, they will likely not get the right cam. Marine cams are tricky. They must have very flat torque curves while not allowing water reversion into the engine. Most cams that are not specifically designed for marine engines perform poorly and/or ruin the motor with reversion.

If the motor mounts are the same with both engines, you have the exhaust, coupler, and all accessories, I think the switch to the 5.0 would be easier and give you better performance. The issue here would be more about the condition of the 5.0.
 
Great points guys; thanks for tips.

I had made up my mind last night to go with the 4.3 rebuild but after calling the place that has the 5.0 I am still going to make the 120 mile drive out to look at it this morning. I found out that it is not a carb but it's fuel injected and a full Vortec and has more hp than I thought it did so it might be worth a look. I have been assured that there is no swap issues between going carb to fuel injected and that it is still a "drop in" application.

My preliminary thoughts were wrapped around the wallet and the best prices I found were:

$5,995 for a 5.0MPI (includes a 100+ lb weight gain)
$4,295 for a carbed 5.0 (includes a 100+ lb weight gain and only 15 more hp)
$4,150 for a carbed 4.3
$2,295 for a 4.3 longblock

Then yesterday I found the other two options;
$2,500 for a used fuel injected 5.0
$1,500 for a local rebuild of my 4.3

The local rebuild shop builds all types of engines but they do a lot of marine engines and all of the mechanics at the marine shop I talked to send all of their work and all of their personal boat engine builds to that shop; so I was assuming that it would know how to rebuild marine engines. I could be wrong though; they might just rebuild with auto cams/etc. The mechs I talked to yesterday had all built gofast boats and had that shop do the engine customization for them but I suppose that doesn't necessarily mean that shop builds for cruising longevity since as we all know building something to go fast doesn't have a thing to do with building something to cruise for years. If I choose the rebuild option I will have to make sure what they're going to do during the rebuild.

I originally had written off the used 5.0 because it's a hundred pounds heavier and I thought only 15 hp more, but now I found out that it's a full Vortec, fuel injected, and has more power than that - and from what I'm told Mercruiser rates hp differently now than they did in '93 and the true hp difference would be even greater.

I also have a strong suspicion that in a boat of this size, a fuel injected 5.0 will probably get better fuel economy than an overstressed 4bbl 4.3 that has all four of its barrels kicked in almost 100% of the time. If true, a 1/3 mpg improvement would pay for itself in fuel costs in a couple of summers.

I've also just now thought of another angle - resale value. Sometime I'm going to want to sell this boat and how hard is it going to be to sell something this size when the potential buyer finds out it just has a "little" 4.3 in it? I would think the 5.0 would greatly add to its resale value more than the extra $1k it will cost me and make it a lot easier to sell quickly. But - it's used and in unknown condition.

I'm leaving in a little while and will let you guys know whether I brought home a 5.0 or not in the next day or so.
 
:cool:

The 5.0 mpi would be a good option and is just about as bullet proof as it gets. That 305 motor has been a main stay in Chevy for 30 years. Hard to beat that one. :thumbsup:
 
Well if your going to get a V8 then at least make the thing fast...........here's something to get you thinking about mods. :grin:

2005_sterndrive_hp_575_sci.gif
 
Tough call. Is it possible to get the V-8 bench tested before installation to verify condition? With the 4.3 you'll always be thinking "I could have had a V-8."
 
Dave S said:
Well if your going to get a V8 then at least make the thing fast...........here's something to get you thinking about mods. :grin:

2005_sterndrive_hp_575_sci.gif
Click to expand...

Think I can get that in MS Judy. Talk about a fast 240SD. Is that what you had in yours Dave :lol:
 
If you go with the 5.0L you will now have an ECM, make sure your gauges are compatible with electronics, they are sometimes picky what you connect to them, some analog instruments can kill an ECM. I take it that the ECM is part of the engine package, get an electrical schematic to be sure you connect the wiring in the proper places. It may be that you can just plug the existing wiring in and go I do not know, just check it out to be sure. Good luck, it sounds like a good move to me. :thumbsup:
 
If you do go the V8 route, I wouldn't fool with the 305, the 350 is dimensionally identical to the 305 and shouldn't be hard to find.
No replacement for displacement
 
midway said:
If you go with the 5.0L you will now have an ECM, make sure your gauges are compatible with electronics, they are sometimes picky what you connect to them, some analog instruments can kill an ECM. I take it that the ECM is part of the engine package, get an electrical schematic to be sure you connect the wiring in the proper places. It may be that you can just plug the existing wiring in and go I do not know, just check it out to be sure. Good luck, it sounds like a good move to me. :thumbsup:
Click to expand...

I agree with Nolan. If you get a later model ECM that interfaces to the instruments via a Smartcraft Gateway, you may be flat out of luck. Again Gerald................a call to the dealer about this would be in order.
 
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