Mercruiser + 4.3 thinking about radical swap to LS1, any help?

C

charliediss

New Member
Jul 15, 2010
9
Algonac, MI
Boat Info
1988 Sea Ray Seville
Engines
4.3l V-6
Well, the old 4.3 is shot and needs to be replaced. Speaking from my "car guy mentality", I have decided to upgrade the V-6 to an LS1 V-8, as it is about as light (all aluminum), and has significantly more power. Does anybody have any practical experience with this? Is there any master resource that can point me in the right direction?:smt100 Any help would be greatly appreciated.

Thanks in advance.

Charlie
 
some of the ski boats a few years ago had the corvette engine as their power plant. AS you know many its parts would need to be changed in the stock engine to make it a true marine engine.. the cam for the street would not work in a boat, as well as the starter , freeze plugs, and on and on
 
Interesting. I knew about the cam, however I did not know about the freeze plugs...this makes me wonder what else I will need to swap. I just want to start the research now, so when I get around to this in a couple of months I will have a good idea as where to start. Which ski-boats ran the Vette engine?
 
As far as those Vette engines: I think you may find most of those 260 Mercrusers were all Vette engines. I believe Merc used the Ram Jet allot.

The LS1 is quite the little Mighty Mouse. The 5.7 version will easily make 400 + HP.

A marine cam is pretty much a mild street cam. Nothing too radical.

Marine soft plugs are just brass ones. I would think the steel ones would hold up around the Great Lakes (bottled water). Putting in brass ones would be no big deal. Weve got 30yr old boats up here still running the original exhaust manns!

GM Performance parts use to have crate motors for hot rods. The PCM had no drive train control, just motor.

There use to be a hack program called LS1-Edit. You could rewrite fuel, timing, everything in the PCM and reflash it. O2 simulators are also available but with LS1-Edit you can just keep the thing in open loop and not need any oxygen sensors. I use LS1-Edit in my 99 hot rod and it works very well.

LS1-Tech is the place to get allot of tuning info.

The intake is composite! If somebody doesn't offer a marine thermostat manifold, you may have to fab one.

I wouldn't be surprised if the exhaust bolted rite up.

The ign shift cutout switch may be a challenge. The FI boat engines of today do it some how?

Interesting concept...
 
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Are you going to run this through the original alpha one drive that came with the 4.3 motor? I seem to recall that they tried putting 330 hp through them around that time and they had a habit of not living very long if run hard.

What kind of shape are your stringers and transom in (any rot or soft spots)?
It sounds like a fun project, so long as the other structural systems/driveline parts are up to handling that much power and torque.
 
An aluminum engine should have closed cooling. Raw water will damage aluminum since even fresh water does not have the required corrosion inhibitors.
 
It sounds like a very cool idea, but you probably should compare it to other re-power options to make sure it makes sense.

For example, a Mercruiser 350 Magnum may work just as well in the boat and be less work and money.
 
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I believe you'll have to check your outdrive gear ratio as well.
 
Frank's warning about corrosion is spot on. Also, a marine cam is an important animal. Not only is the torque curve important, but you have reversion issues as well. I'd go with a 350 Mag as well.
 
terminaldegree said:
Are you going to run this through the original alpha one drive that came with the 4.3 motor? I seem to recall that they tried putting 330 hp through them around that time and they had a habit of not living very long if run hard.

What kind of shape are your stringers and transom in (any rot or soft spots)?
It sounds like a fun project, so long as the other structural systems/driveline parts are up to handling that much power and torque.
Click to expand...

Yes sir, my intent...as of today...is to run the existing drive (any suggestions on an upgrade?) My stringers and transom are in excellent shape, just recently checked them out. I am really excited to get started on this thing.
 
All electrical components will need to be swapped so they are ignition protected (starter, alternator, ECM etc)

ECM could just be located away from engine compartment. I agree a 350 mag would be easier.
 
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keokie said:
Frank's warning about corrosion is spot on. Also, a marine cam is an important animal. Not only is the torque curve important, but you have reversion issues as well. I'd go with a 350 Mag as well.
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Interesting. I will hit the books this weekend and see what...if any...options are available for the LS1 marine world. I think if my only reasonable option was a Mag, I might just go back with the 4.3...do you know the output of a mag and merc?
 
charliediss said:
Interesting. I will hit the books this weekend and see what...if any...options are available for the LS1 marine world. I think if my only reasonable option was a Mag, I might just go back with the 4.3...do you know the output of a mag and merc?
Click to expand...

Merc 350 MAG is 300hp (http://www.mercurymarine.com/engines/inboards/sterndrives/mpi350.php)

the Merc 4.3L is 220 (http://www.mercurymarine.com/engines/inboards/sterndrives/mpi4-3l.php)

Not sure whats the story with this but you could do the 377 MAG which is 320 (http://www.mercurymarine.com/engines/inboards/sterndrives/377mag.php)
 
One nice thing about the 300hp 350 Mag is that Mercruiser used the Alpha One behind this motor.

Any more power, and the reliability of the Alpha will be questionable.

Your Alpha One should have a 1.62 or 1.81/1.84 ratio. Those are the 2 most common ratios behind a 4.3. The 1.62 will work well with a V8, but you might have a hard time getting the right prop pitch if you use a 1.81/1.84 drive behind a V8.

The Sea Ray online prop chart should tell you what ratio you have.

Regardless, I bet your boat would run great with a 350 Mag. I don't know the specifics of your boat, but a 10-15 mph top end increase over the 4.3 seems plausible.
 
The 350 Mag is rated at 300hp at the prop. Car and crated motors are rated at the flywheel. To the prop will drop horsepower 12-20 percent.

A 350 mag will be a very noticeable improvement over a 4.3 and should essentially be a plug and play installation.
 
mvoellinger said:
Which outdrive do you have? The Alpha One will work with the 4.3 or the 350, but the 377 needs a Bravo.
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I believe it is the Alpha one outdrive, as I want to say my boat mechanic was throwing that around during our last meeting. Which is the 377? Is that also considered a magnum?
 
Ok, I just wanted to get some opinions here on the valuation of this swap. To me, a first timer, it feels as though someone is taking advantage of me.

The final price is $6,000 for the crate engine and installation! And that is a direct swap with a 4.3 and no upgrades. He charged me $600.00 just to remove the engine and inspect it. I sure feel like I have been HAD.

Any thought?
 
charliediss, Take a look at performanceboats Get into the LS1-LS2 forums. They talk about stainless exhaust for LS1 for boats for under 200.00 and intakes that will use boat carbs. Interesting reading. Good Luck on the swap.
 
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