MerCruiser 4.3lx shortblock compatibility?

[Gibbles]

Well I recently bought a new to me boat, and I got one with a crack in the block!

what I have is a 1994 4.3lx with the 4-barrel carb.
Much of the details I'm still not sure about, however I'm weighing the idea of upgrading to actual Vortech heads, and the Edelbrock manifold...

I see many short block and long block options if I were to buy one already rebuilt, or just to buy a truck engine and rebuild it.

So, I guess my question is,
Are there any compatibility issues with the alpha 1 gen 2 out drive, or other things like if I decide to run the current cylinder heads on the newer block?

One thing I'm looking at is a block from 1997 - 2003 from a donor S10, or just a short block from an ebay seller (where I would go through that thing with a fine-tooth comb)

I'm assuming the bell housing and engine mounts will be the typical GM product and have a nice solid standard throughout the years?

I did read/skim over this: https://forums.iboats.com/threads/1990-mercruiser-4-3-same-as.769899/

And it almost sounds like I might be better off picking up a later donor engine?
Or at least plan on replacing the front cover?

 

[Scott Danforth]

Block doesn't care what heads. Only the intake cares

Drive doesn't care what heads, only cares about what flywheel

Main difference between the 1993-1995 motor and the 1996-2003 motor is the heads (and plastic oil pan)

If you get a motor from an s-10. You only get the short block and heads. The rest you can not use

You need to swap the core plugs go brass or stainless. You need marine head gaskets, marine water pump, all the marine bolt on bits.

4.3 from your local LKQ salvage yard is about $150

Some light reading. https://forums.iboats.com/threads/complete-history-of-the-4-3-liter-with-casting-numbers.693935/

 

[Gibbles]

Ok so if I did go with a later 97+ short block and re-used everything from 1994..

I would need to get the later front cover and probably oil pan?

 

[Scott Danforth]

If you got a 1996 or later vortec. I would look at a billet aluminum front cover and a custom oil pan. Use the marine accessories from the 1994. Buy manifolds.

If it was me, I would go V8. Same work, same cost, more power

 

[Scott06]

Have to agree with Scott. While a vortec head intake and carb swap will gain 20-30 hp if you have a 22 ft boat just get a 5.7. I did a 4.3 to V8 swap. Since the front and back of the 4.3/5.0/5.7 blocks are the same, you can keep a lot of your accessories and piece it together easily. Certainly more money than a head swap but i have yet to own a boat with too much power

 

[Lou C]

I have thought the same thing 4.3 to 5.7 swap while it’s more money for certain things I have a heavy 20’ boat approx 4200 lbs. My Cobra drive ratio is 1.68:1. Currently using a 15x17 prop I wonder if I could do the V8 swap with the same drive and a 21 pitch prop? This boat definitely came with a V8 option so the engine mounts are big enough. The Horizon 200 came with a 5.0 but the 201 Liberator (same hull different top cap), came with a 5.7 King Cobra.

 

[Scott06]

I have thought the same thing 4.3 to 5.7 swap while it’s more money for certain things I have a heavy 20’ boat approx 4200 lbs. My Cobra drive ratio is 1.68:1. Currently using a 15x17 prop I wonder if I could do the V8 swap with the same drive and a 21 pitch prop? This boat definitely came with a V8 option so the engine mounts are big enough. The Horizon 200 came with a 5.0 but the 201 Liberator (same hull different top cap), came with a 5.7 King Cobra.

Yes probably. I kept my V6 drive (1.81) with the 5.0 (stock except for intake and Edlebrock 1409) that should have by the factory had a 1.62 drive.

I had to go up from a 19" pitch to 21" pitch. If I knew then what I know now I would have done a 5.7 instead of a 5.0. Boat was not offered with a 5.7 and I wanted to keep the drive as the boat had 37 hrs on it when the PO cracked the block. It works great, but when I have a full boat of now adults ,as the kids have grown, and pulling a skiier the extra 30-40 hp (for the same engine cost) wouldn't hurt...

Its even easier of your boat was offered with a V8 like mine as engine compartment and stringers will likely be set up already.

 

[Scott Danforth]

The OP's 22' islander sure could use a 5.0 or 5.7

 

[Gibbles]

Brings me up to another thought, aluminum block LS?
I sure would like EFI...

but that sounds like a ton of work.

 

[Gibbles]

then I also have to think about gear ratio in the outdrive right?

 

[Scott06]

then I also have to think about gear ratio in the outdrive right?

Yes but you can likely prop around one or two steps in outdrive ratio like I did. What I surmised from my repower is each ratio step is approx 2" in prop pitch. This allows the boat builder to keep all different hull and power train configurations basically working within the 15"-23" 'normal' pitch range. The gear ratio is in the upper half of your existing OD so worst case swap an upper

I would stay away from LS and injection unless yo u have deep pockets and the skills/experience needed. The V8 was suggested because of the boat size and the common lineage between a SBC and the 4.3- so you can reuse a lot of the accessories on your existing bobtail. By far the easiest is heads and a vortec intake on your existing short block. This by far saves the most of your existing set up (exhaust manifolds).

Do you currently have a 2 or 4 bbl carb? non vortec 4.3s ate 175 and 205 hp for 3 and 4bbl respectively. Vortec 4.3s are worth 190 and 220 hp respectively

 

[Gibbles]

Yes but you can likely prop around one or two steps in outdrive ratio like I did. What I surmised from my repower is each ratio step is approx 2" in prop pitch. This allows the boat builder to keep all different hull and power train configurations basically working within the 15"-23" 'normal' pitch range. The gear ratio is in the upper half of your existing OD so worst case swap an upper

I would stay away from LS and injection unless yo u have deep pockets and the skills/experience needed. The V8 was suggested because of the boat size and the common lineage between a SBC and the 4.3- so you can reuse a lot of the accessories on your existing bobtail. By far the easiest is heads and a vortec intake on your existing short block. This by far saves the most of your existing set up (exhaust manifolds).

Do you currently have a 2 or 4 bbl carb? non vortec 4.3s ate 175 and 205 hp for 3 and 4bbl respectively. Vortec 4.3s are worth 190 and 220 hp respectively

4bbl carb currently.
That also raised another question I had for the edlebrock 4.3 marine manifold for the 4.3, It's not clear if I can use the same carb, or if I need to buy theirs?

I also located a "Core" 4.3 out of a 97 S10 for $30.
If I get lucky, I might have a donor for the vortec heads, and if I get really lucky the block is rebuildable.

 

[Lou C]

I would never advise anyone to do EFI in an old boat. The parts cost and complexity of wiring & added failure points are a deal breaker for me. Simple 4 bbl carb feeds a Chevrolet just as well now as it did 50+ years ago. Parts for a Holley, Edelbrock or even a Quadrajet are available and inexpensive.

 

[Scott Danforth]

I would avoid EFI in a boat for many reasons. You have to use Marine EFI (very expensive), and it doesn't make more power or better economy

If you use an aluminum motor, you need to run a heat exchanger

 

[Scott Danforth]

I also located a "Core" 4.3 out of a 97 S10 for $30.
If I get lucky, I might have a donor for the vortec heads, and if I get really lucky the block is rebuildable.

You can get low mileage running 4.3 motors for under $200

 

[Gibbles]

Biggest thing I like with efi, the idle air control.
None of this trying to rev the engine to keep it running, or to get it started.

 

[Scott Danforth]

Biggest thing I like with efi, the idle air control.
None of this trying to rev the engine to keep it running, or to get it started.

then you didnt tune the carb right

 

[Gibbles]

That said, I think the control I have needs some repair.
I can't get the gear change select to bypass by pressing the button on the side of the handle.

future tinkering to figure it out.

 

[Scott Danforth]

FWIW, I start a big block without a choke and dont have start issues or idle issues. throttle to 1/3 for the first 30 seconds or so for it to clear its throat. then as I deal with lines, etc, the motor warms up to about 120, and I am off

I used to runt a 360 mopar without a choke in wisconsin winters as a daily driver. would have to blip the throttle when braking for the first few intersections until the temp got over 100

 

[Lou C]

That said, I think the control I have needs some repair.
I can't get the gear change select to bypass by pressing the button on the side of the handle.

future tinkering to figure it out.

Once you figure that out it’s likely your problem will be solved. On my 4.3 4bbl QJet I pull the OMC control out to disengage the shift system that allows me to pump the throttle & set the fast idle. I let it warm up at 1200 rpm, while I’m taking off the canvas putting up the Bimini and getting my tunes on Spodify…not too different from when I started driving in 1972!