Mercruiser 4.3

[Sean]

Okay, so with the issues on my old Merc 165 IL6 I am considering a power upgrade to a mercruiser 4.3 V6 / alpha.

I have found several "donor" boats that are in decent shape at a decent price however, the majority have the 2bbl 4.3 pushing 175HP. Spending the $$$ for an upgrade I would hope would add greater power as well as reliability and other benefits of using a more current powertrain.

The 4.3 220HP MPI is still too new and is cost prohibitive but, there are some 4.3 205HP motors available (more scarce) and my thought are as follows:

1) Is there a difference in performance (you can feel) between the 175/180 2bbl version and the 195/205 4bbl version?
2) What is the fuel consumption difference?
3) Other than the carb what are the differences between a 175HP and the 206HP engines?
4) Are there performance upgrades (kits) that can be done to a 175 HP motor to better maximize its potential.

At the end of the day I dont want to spend all this $$$ to move from an inline 6 to a V6 and 10HP....but 200+ looks to be worthwhile.

What's the best way to go?

 

[nathan]

there will be a lot less torque from the v6 compared to the inline 6 engines. there will be more torque with the two barrel. not sure if you will see much better gas mileage with a single barrel because as you will probably be hammer down more of the time. a v8 would be more fun and would probably better gas mileage as the v6 engines are usually gas hogs.

 

[Sean]

Not sure if I have the clearance under the hatch for a V8. There might be a weight issue also and more potential issues relocating the fuel tanks if I move to a SBC.
I'd LOVE to stuff in an aluminum block V8 but I have not won the lottery yet.

My buddy has a similar Greavette with a 4.3 V6 @ 205HP. He runs a four blade stainless prop and has a nice holeshot and decent mileage. I would like to emulate that.

There's just so many 4.3' (175HP) boats available cheap <$3000 that have everything needed for the swap. The only 205 HP doner I found is $5000....and the couple ob 260HP V8's have been north of that with lots of hours on them.

 

[Sean]

Current 165 HP IL 6 engine/drive weight 715lbs...
SBC 260 HP V8 /Alpha = 890 lbs
4.3 205 HP V6 / Alpha = 665lbs.

 

[nathan]

makes since I would go with a two barrel.

 

[Sean]

I would LOVE the 4.3 MPI @ 220 HP....but I don't need another mortgauge on my house.

So, does anyone know how to make a 4.3 175HP in to a 205HP ?

 

[Fun Times]

I would LOVE the 4.3 MPI @ 220 HP....but I don't need another mortgauge on my house.

So, does anyone know how to make a 4.3 175HP in to a 205HP ?

The only difference is the carb, intake manifold and the needed throttle linkage.

http://www.mercruiserparts.com/selectDocs.asp?doc_nbr=17468

What years are you looking at?
http://www.mercruiserparts.com/selectModels3.asp?type_id=V6

 

[Sean]

Wow that's it?
who'd a thunk just that would net 30HP!

Looking at an '88 and an '89.

UH oh...looks like most of those upgrade parts are NLA.
probably best to hold out for the "real deal".

Unless...

Does anybody make an aftermarket kit?

 

[Sean]

Holy smokes! There is alot of info on this upgrade / swap online....
Looks like Edelbrock makes the carb and manifold.

Alot of talk about Vortech heads too. Not sure yet how much of a part they play....

 

[Fun Times]

Holy smokes! There is alot of info on this upgrade / swap online....
Looks like Edelbrock makes the carb and manifold.

Alot of talk about Vortech heads too. Not sure yet how much of a part they play....

I don't recall how much extra H.P you get with the vortec heads, but from what i have read on the online boating forums, everyone that has done it, LOVE IT.

Yes edelbrock would be the way to go for aftermarket performance, But of course like any upgrade it cost $$$$$$.

When you look through the link/s, all the parts will show/tell you what engine uses what between the 175/205.

Other engine vary on what part are different, for example 5.0L vs 5.7L, Internal carb size, engine control module, etc, etc.

Vortec heads use different size spark plugs then non vortec.

 

[Sean]

Well, I went for the whole 9 yards....
Vortec heads, Edelbrock 600cfm 4bbl carb and performer manifold. A mild porting job, 1.6 rockers....and I'm debating a new bumpstick.
I'm expecting numbers in the 225 HP range.

 

[nathan]

that boat should move with that motor in it.

 

[Sean]

That's the plan!

 

[Sean]

Got news from the macine shop yesterday...
the heads have now been cleaned and magnafluxed...no cracks. perfect specimins.

I talked to Marine Kinetics about a cam to get the most out of this motor. They advised against opening the exhaust to 1.6 so to keep exhaust velocities up. Will still be going to 1.6 roller rockers, adjustable studs and doing some clean up porting.

Will wait to pull apart the bottom end (and see what we have) before deciding on a cam to take full advantage of what configuration we end up with.

 

[nathan]

sounds like a great starting point.

 

[Sean]

Okay, so the bottom end was perfect. Just freshen her up a bit...
To summarize where we are, here's the powerplant/drive:

rebuilt stock Mercruiser 4.3L 90* V6
rebuilt Vortech heads (heart shaped combustion chamber) clean up of ports.
Edelbrock 2114 dual plane manifold
Edelbrock 1409 600cfm carb (with 262 cid kit)
IMCO Thumper Power manifold/riser
Quicksilver 431-803186 camshaft
1.6 roller rockers

We'll have to dyno this thing for giggles when it's done.

Now I wish someone made a diverter for the 4.3 V6 but I cant find one....so the exhaust will go through the prop.

Stock alpha drive...looking at a stainless HIGH FIVE prop.

 

[Sean]

I also sent out the gimble to be disassembled (so I can paint it) and rebuilt. There's no sense in going half way now. Plus, I wanted a professional to do the gimble assembly....that's a big hole back there.

I think I will most likely need a remote oil filter and possibly fuel too. Also probably changing the fuel tank layout. Moving to dual tanks.

 

[Sean]

Okay, it looks as though Hardin Marine make a diverter system that'll fit a stock 4.3.
The IMCO Thumpers are out because thay cannot use a diverter system.

So Exhaust is the big question now...and it's come down to GLM (inexpensive) cast aluminum, but with some dodgey reviews...or Hi-Tek Matine and their beautifully made stainless performance units (that cost a small fortune).

Thinking I might as well put on some trim tabs while I'm in there and can make the room.

 

[Fun Times]

So Exhaust is the big question now...and it's come down to GLM (inexpensive) cast aluminum, but with some dodgey reviews....

Just be aware that GLM stands for Good Luck Marine.

They have a tendency to leak a lot, also beware of the green leakers.

http://forums.iboats.com/showthread.php?t=537414

Good luck, no pun intended.

 

[Sean]

My nachineinst says he will true all surfaces before we assemble...I'm more worried about cracks and poor castings. I asked the GLM question on the DONZI registry...and there are several there that swear by GLM!