V-6 to V-8 conversion

[luv2b0at]

I am going to have to dig into my 1983 OMC 3.8 V-6 to figure out what is knocking. If it turns out to be a big problem, I am interested in possibly replacing the entire engine. I have some room in my engine compartment and could change to a V-8. I would assume there are newer 4 or 6 cylinder engines that have similar or better horsepower as the engine I currently have. I am not looking to double my speed or anything. I just want something reliable and close to what I have now.

My drive unit is a Stringer Manual Shift. I know all the negative swtuff about the stringer, but mine is working well. Is it difficult to change over to a different type of motor? What do I have to look for in choosing a motor that will connect easily to the drive?

Any suggestions or comments are appreciated including the possibility of changing over to an outboard. The 200+ HP outboards appear to be much smaller and lighter than an entire inboard type engine.

 

[chiefalen]

Re: V-6 to V-8 conversion

You know the more modern V-6 gives close to a V-8 305.

Easiest way to go 4.3 200+ Hp. Votec why not, see them on ebay all the time.

Maybe a crate motor ?

New manifolds and riser the 400 dollar special.

 

[luv2b0at]

Re: V-6 to V-8 conversion

Will it bolt right up to the drive as is or is there something more I will need.

 

[chiefalen]

Re: V-6 to V-8 conversion

Might have to just change out the flywheel and the coupler of course should all be a perfect fit the bell housing adapter should fit .

 

[chiefalen]

Re: V-6 to V-8 conversion

This being a stringer you don't need to even pull the drive.

When you pull the motor The drive will tilt down naturally you might want someone holding it on the outside and letting it down gently so it don't bind the shaft.

Let me see if i have the thread ill post it.

http://forums.iboats.com/showthread.php?t=280334

 

[luv2b0at]

Re: V-6 to V-8 conversion

Thanks. I'll be looking into it. I am assuming better knots per gallon as compared to what I have now?

 

[chiefalen]

Re: V-6 to V-8 conversion

I don't know if you know this but the manifolds are interchangeable between both.

If the 3.8 is good i would keep it a darn good motor.

But the 4.3 WILL be a straight change out. Seen them on e-bay right now new marine motors. Or as i said before a crate motor.

 

[luv2b0at]

Re: V-6 to V-8 conversion

I'll know more once I get into the current engine I have in the boat. It's knocking so it may be just a lifter. I have very black water (not oil, it's like it's tainted with exhaust) in my bilge at the end of the day so I will be looking for a leak in the exhaust manifold areas or a crack somewhere. I would like a bit more power as it's a pretty heavy boat (500 lbs dry and empty). Putting 4 bbl on the current one will cost a bit.

 

[chiefalen]

Re: V-6 to V-8 conversion

Knocking gonna be the lower end. Smokes alot?

 

[rdj59]

Re: V-6 to V-8 conversion

Does the omc outdrive use a bellhousing to attach to the motor? Reason i ask is if the 3.8 is a buick it will have a different blot pattern than a chevy. If this is the case then buick 350 is what you would want. It will bolt in place of the 3.8. It will even use the same mounts. But the only problem which is a deal breaker is that you probably won't find marine manifolds for it as i don't think one was ever used in a marine application.

Jeramie

 

[Howard Sterndrive]

Re: V-6 to V-8 conversion

if the 3.8 is a buick it will have a different blot pattern than a chevy.

It's a Chev 3.8, Jeramie

I don't know if you know this but the manifolds are interchangeable between both.

sort of-

the port spacing is the same on a 229 or 262 head, so they would technically bolt to the head....
But if the 3.8 manifolds are the original OMC ones, they wont clear the valve covers.

I'd just fix the 3.8 ... with the marine cam, those 229's make good power and they are good on fuel

 

[chiefalen]

Re: V-6 to V-8 conversion

I like the 3.8 also like Howard posted. But me, if i were dropping a new motor in then i would go with new manifolds and risers, you would be good for another 20 years and never sell the boat.

Bottom line i would try with every once of skill that i posses to keep the 3.8.

But thats me, you might just want to go with fresh everything and i can understand that also.

And this is where you can get the new manifolds and risers all comes in one box and the gaskets too.

http://amarket.com/omct.htm

 

[luv2b0at]

Re: V-6 to V-8 conversion

The knocking was light at first and has gradually gotten louder even with miracle oil running in it.

It does not smoke. We'll be pulling the valve covers to have a look in a week or so That will tell us more.

I put all new manifolds and risers on it a year ago.

 

[chiefalen]

Re: V-6 to V-8 conversion

Ok new manis last year with risers, last year.

I know for a fact pre vortec V- 6 the manis will fit cause it's the same part numbers.

Vortec might not clear like Howard posted but pre-vortec will. But if all we are talking about are valve covers there got to be way around that.

I tell you what, before i start seriously investigating the way around let's see what you discover the reason for the knocking is. And what your decision to resolve the situation.

One Chief to another theres a solution.

 

[Howard Sterndrive]

Re: V-6 to V-8 conversion

I know for a fact pre vortec V- 6 the manis will fit cause it's the same part numbers.

1985 was the first year OMC used the 4.3, the first year Chevrolet made it, and it used different part number manifolds than the 3.8.
The 4.3 used 1 piece manifold/riser.
3.8 used 2 piece manifold and riser.

1985 3.8:

1985 4.3:

The valve cover of a 4.3 won't fit in under the curve of the 3.8 manifold casting. And if you remove the valve cover, and try to mount the manifold, you'll find the rocker arms actually hit the manifolds.

The Osco aftermarket, OMC 1 pc. or Merc style centre riser manifolds will clear the 4.3 valvetrain, but the Merc style will not clear Selectrim engine mounts.

I don't understand the insistence of sticking with bad advice. There is no workaround. The 3.8 OMC factory manifolds do not, under any circumstances, fit a 4.3 of any vintage. period.

If you go to a 4.3, you must go to the 1 pc. OMC, or Osco V6 manifolds.

 

[chiefalen]

Re: V-6 to V-8 conversion

Another reason to keep the 3.8, the ole Chief must have done a different make swap.

Don't know what the manifolds gonna cost and one piece, no good.

Checked the numbers myself, 910156 , 98422 different numbers.