120 hp to 4.3 l swap - some info needed

[GiMLit]

Hey folks
Hoping someone can help me with some info.

I am looking at purchasing a 18 ft Cobia Bowrider 18VBR I/O
Here is the scoop.
Original engine removed 140 hp 4 cyl (reason from what I gather is a bent pushrod acording to current owner.)
He has installed a 4.3 L V6 from a Chevy Sonoma.
This motor will need to be removed to be rebuilt as he has half done the job and left it exposed to rain etc and the motor turns over but is full of water. Anyway that isn't the reason for this thread.

Can anyone tell me if they know of specific issues I may run into? He has the Volvo Penta Exhaust manifolds and the thermostat housing etc....

A place with info to help me along to complete this swap?
The current engine is throttle body injected. Better to run a carb and reason?
Omc outdrive is a 980707 any issues with it handing the 4.3 vs the 120 hp 4 cyl ( I assume it would have been a 2.5 L ) ?

Thanks in advance.

 

[Don S]

Re: 120 hp to 4.3 l swap - some info needed

Can anyone tell me if they know of specific issues I may run into?

Basically, it's dangerous. It doesn't have a CG certified electrical system or fuel system approved for marine use.
If that isn't bad enough, the ECM is set up to handle automotive. Boats don't work like that. Starting with a cam, then lots of other things are off.

The drive is also a problem, you have the wrong gear ratio, and just changing props isn't going to help. The drives for the 120's also used a smaller gearcase and lighter gears. Wouldn't hold up to the 4.3, even if it's automotive.

 

[MikDee]

Re: 120 hp to 4.3 l swap - some info needed

We need more info, what year is the motor, I believe 96' and newer has the good vortec heads!, fuel injection is computer controlled along with the oxygen sensor, usually found on a truck, or car, you may not be able to use this on a boat? If it's not a marine engine, you'll need stainless head gaskets, & brass freeze out plugs for the head, & block, and you need a starter, alternator, fuel pump, & carburetor, that are marine specific, emitting no sparks or fuel vapors. Finally, your outdrive will hold it but the gear ratio is probably wrong, 2:0X1 reduction gearing, you need 1:50X1 reduction gearing, to get a prop in a usable pitch range. That's just to start, I'm sure there's more, are you sure you want to go through with this?

 

[GiMLit]

Re: 120 hp to 4.3 l swap - some info needed

Thank you for your advice and opinion.
I am going to look at the parts he has kicking around. All the manifolds are new so maybe if I go back to the 3.OL I can sell them to make some $ to ofset my investment. I am making sure I get the original 3.0L engine if I buy it. That way I can swap back to it if that is the way I fel it should go.

The 4.3 sure would make it hall butt compared to the 3.0 L.

I am a auto mechanic and have been around racing and cars my entire life Yikes 40 years........so it isn't like am a newbie to engine swaps but marine application is new to me.

I have 1 question about your comment regarding the drive. The model # is 980707 and I have read a few threads with that same # being matched with a 5.0L, would the internal components be differnet?

Again thanks for the info and I appologize for my ignorance regarding marine. I only got the boating bug very recently after helping a friend repair and fine tune his 120 hp i/o Mercruiser and then swapping my dads 50 hp outboard Johnson with a 75 hp Johnson that I picked up and repaired. This is all in a span of 4 weeks.
Other than that I have had a few rides in power boats but never owned one or worked on them.

 

[GiMLit]

Re: 120 hp to 4.3 l swap - some info needed

We need more info, what year is the motor, I believe 96' and newer has the good vortec heads!, fuel injection is computer controlled along with the oxygen sensor, usually found on a truck, or car, you may not be able to use this on a boat? If it's not a marine engine, you'll need stainless head gaskets, & brass freeze out plugs for the head, & block, and you need a starter, alternator, fuel pump, & carburetor, that are marine specific, emitting no sparks or fuel vapors. Finally, your outdrive will hold it but the gear ratio is probably wrong, 2:0X1 reduction gearing, you need 1:50X1 reduction gearing, to get a prop in a usable pitch range. That's just to start, I'm sure there's more, are you sure you want to go through with this?

Welllllllllll.
I am not exactly gifted in financial terms but as far as mechanical ability it call can be done but at what cost ????
I don't mind the labour as I would be picking this boat up for very cheap (or I won't be picking it up at all.)
gear ratio and cam specs were my first thoughts as well as messing with injection and ecm etc..... Can I do it ........... I am certain I can but that isn't the point.
A carb in my opinion is better for this application. Then I need a manifold to bolt it onto........ messing with gear ratios in a drive I have never played with I don't see being a good step as a first project.
Keep the info coming. I am soaking it all up and my first reaction was to rebuild the 3.0L and reinstall it and it looks like this maybe my best way to go.

 

[GiMLit]

Re: 120 hp to 4.3 l swap - some info needed

Another Question.
REAL IMPORTANT ONE!!!! Engine rotation is ?????? standard clockwise or CC ????

 

[95yj]

Re: 120 hp to 4.3 l swap - some info needed

All sterndrive engines are standard rotation meaning looking at the flywheel from the back of the engine it is turning counter clockwise.

 

[MikDee]

Re: 120 hp to 4.3 l swap - some info needed

Welllllllllll.
I am not exactly gifted in financial terms but as far as mechanical ability it call can be done but at what cost ????
I don't mind the labour as I would be picking this boat up for very cheap (or I won't be picking it up at all.)
gear ratio and cam specs were my first thoughts as well as messing with injection and ecm etc..... Can I do it ........... I am certain I can but that isn't the point.
A carb in my opinion is better for this application. Then I need a manifold to bolt it onto........ messing with gear ratios in a drive I have never played with I don't see being a good step as a first project.
Keep the info coming. I am soaking it all up and my first reaction was to rebuild the 3.0L and reinstall it and it looks like this maybe my best way to go.

If you're running in fresh water, I wouldn't worry about the marine gaskets, & such, but remember they may not last as long, saltwater it's mandatory, the 4.3 long block, & heads, is a good starting point, and the cam should be fine, but for safety's sake the external part's, need to be marine. If that's a late model 4.3 it maybe hard to find a carb, & manifold for it to bolt up, but you could get a late model marine unit for a hefty price though, unless you find one on e-bay. I would think the drive should hold up fine, but the gearing will be like having a (4:11, or 4:56 rear in a car), you would probably be fine with the right prop, but it would need to be a high pitch, like 23" (usually as high as they go normally), after that it's usually custom to keep your revs down into the 4200-4600 rpm range, but wait! a 4blade prop with a high pitch like 22 or more, may keep the rpm's in check without your motor running over revved, and give you more power to boot!

 

[whywhyzed]

Re: 120 hp to 4.3 l swap - some info needed

The 4.3 sure would make it hall butt compared to the 3.0 L.

with the ignition system (advance curve) from auto, and vacuum controls, I would suspect it would probably be slower than the 4 cylinder if the boat even planes at all.

 

[MikDee]

Re: 120 hp to 4.3 l swap - some info needed

I don't think so, with a marine distributor it should be fine, I'd say use an old late 70's, early 80's, Chevy V6 HEI distributor if it's safe, or can be made safe for a boat, and they use mechanical advance, and that can the modified to work in a boat, no vacuum advance is needed.

 

[bomar76]

Re: 120 hp to 4.3 l swap - some info needed

As has been been posted here a zillion times-

YOU CANNOT USE AN AUTOMOTIVE IGNITION SYSTEM IN A BOAT....PERIOD
It's neither SAFE, LEGAL, or SUITED for such usage.

 

[GiMLit]

Re: 120 hp to 4.3 l swap - some info needed

As has been been posted here a zillion times-

YOU CANNOT USE AN AUTOMOTIVE IGNITION SYSTEM IN A BOAT....PERIOD
It's neither SAFE, LEGAL, or SUITED for such usage.

I wonder if you could clarify automotive vs marine ignition system.
The 2.5 l 120 hp boats I have looked at to this point have standard coils, wires, cap etc.... they make a high voltage from a low voltage, doesn't matter how you slice it you have 10,000 volts plus.

HEI from a automotive application is different only in the fact that it uses a pickup and module vs a point distributor for a trigger, heck many automotive applications use a crank pickup.
You have more chance of stray voltage from bad caps, wires and coil towers than anything and those have been on all the inboards I have looked at.
Weight curve for advance would be an issue that is easily rectified with a aftermarket curve kit.

 

[tommays]

Re: 120 hp to 4.3 l swap - some info needed

The marine units have a spark vent screen that allows and fumes from say a bad shaft seal that find there way in there to go bang in a safe way


Vs and auto unit that will blow the cap off as well as set off a secondary explosion from any fumes that may be in the engine area


It is just like the flame arrestor on the carb is there so IF it backfires you do not have a secondary explosion


If you have good luck useing AUTO PARTS you will not kill anybody just mess them up real bad


They really do test the units to get a CG use rating



Tommays

 

[180shabah]

Re: 120 hp to 4.3 l swap - some info needed

OK, to sum it all up, if you keep the 4.3 you will need the following:

Marine distributor - Merc's TBIV is plentiful and dead reliable
Intake manifold - not hard to find, just make sure it matches your heads
Marine Carb - Lotsa choices here, I like the Edelbrock(or Weber clone)
Marine Starter
Marine alternator
Marine water pump
Probably another $400-$1000 in misc. depending on salt/fresh water usage and the gear change in the drive.
Start adding the prices up, then make a decision. Personally, I would be looking for a different boat, one that did not have an OMC on it, but that is probably a subject for another thread.

Good luck

 

[MikDee]

Re: 120 hp to 4.3 l swap - some info needed

As has been been posted here a zillion times-

YOU CANNOT USE AN AUTOMOTIVE IGNITION SYSTEM IN A BOAT....PERIOD
It's neither SAFE, LEGAL, or SUITED for such usage.

You notice I also mentioned a marine distributor! if the HEI can't be converted.

 

[MikDee]

Re: 120 hp to 4.3 l swap - some info needed

OK, to sum it all up, if you keep the 4.3 you will need the following:

Marine distributor - Merc's TBIV is plentiful and dead reliable
Intake manifold - not hard to find, just make sure it matches your heads
Marine Carb - Lotsa choices here, I like the Edelbrock(or Weber clone)
Marine Starter
Marine alternator
Marine water pump
Probably another $400-$1000 in misc. depending on salt/fresh water usage and the gear change in the drive.
Start adding the prices up, then make a decision. Personally, I would be looking for a different boat, one that did not have an OMC on it, but that is probably a subject for another thread.

Good luck

This is the botton line, and the best way to go.

 

[mkpj1]

Re: 120 hp to 4.3 l swap - some info needed

"Run for the hills, Run for your life." (Dio). Nothing that time and money won't fix. You couldn't give me that boat for free! The previous owner left it open to the elements to get water in the engine!! How's the floor, transom??? Tires....etc....etc...Run Forest, Run!

find another boat with a 4.3.

Ken

 

[GiMLit]

Re: 120 hp to 4.3 l swap - some info needed

Thanks everyone for your insight/comments.
Please keep them coming.

Boat is a 1986 18 ft Cobia Bowrider 18VBR
2 issues when I looked at it first, what was done(engine swap) and how and the OMC outdrive.
Both still scare me mostly the OMC.
Without great detail what is the typical issue for th eOMC drives, or is EVERYTHING!!!!


Trailer is in good shape, boat is pretty good along with interior.
$1000 is all I could pay for it in my opinion.
Open to weather........... 24 hrs is too much for an engine to be open.
A boat........ I hope the floor etc....can handle abit of water. It has been draining np and appears in decent shape.

 

[180shabah]

Re: 120 hp to 4.3 l swap - some info needed

First, $1000 is too much money for an old boat that doesn't run.

As for the issues with OMC, there are no major issues with the design. The company has gone out of business. Thus, some of the parts(depending on where you live) can be hard to find and expensive.

Water and boats - Boats like thier water on the outside, not the inside. Most have interiors made of wood, and wood rots.

 

[whywhyzed]

Re: 120 hp to 4.3 l swap - some info needed

"Run for the hills, Run for your life." (Dio).

wasn't that Iron Maiden?