OMC 4.3 V6 dry joint "batwing" conversion exhaust kit

[ccourser]

I am looking to replace my 1989 OMC 4.3 V6 "batwings" with a dry joint system (with hopefully Barr or Mercruiser). I know GLM and BPI offer wet joint kits. From what I read Barr/Mercruiser dry joint manifolds will fit the motor. I am stuck trying to determine the correct part number for the dry joint risers and understand the Volvo Penta (3853372/914936) Upper Exhaust Pipe Elbow Tubes have to be used to mate to the exhaust with the appropriate rubber connectors. Thanks in advance.

 

[Scott06]

I am looking to replace my 1989 OMC 4.3 V6 "batwings" with a dry joint system (with hopefully Barr or Mercruiser). I know GLM and BPI offer wet joint kits. From what I read Barr/Mercruiser dry joint manifolds will fit the motor. I am stuck trying to determine the correct part number for the dry joint risers and understand the Volvo Penta (3853372/914936) Upper Exhaust Pipe Elbow Tubes have to be used to mate to the exhaust with the appropriate rubber connectors. Thanks in advance.

I think @Lou C did this swap on same engine

 

[Lou C]

I thought of that when I converted mine back in 2017, but I thought there could be slight dimensional differences that might cause leaks. So I went with the Barr OMC/Volvo wet joint with the VP 90* down pipes and rubber hoses. Fit fine no leaks…I think I’d have to be able to borrow a manifold/elbow to check for fit, I would like to have the dry joint system….

 

[Scott Danforth]

Mercruiser angles are different than Volvo Penta

 

[Lou C]

That's exactly what I was thinking of, there's a 7*, 10*(?) and 14*, after thinking the whole thing though I felt it was less trouble to use what I know would work.
Also there's the relative heights of the outlet of the elbow, above the mounting points, there is really no way to know if it would work, unless you could get a shop to loan you a manifold and elbow and trial fit it with the hoses, etc.
BTW, I scoped my manifolds yesterday with the inspection camera and they still look good inside, no signs of leaks. No leaks on the outside either. I think I'll run em one more season and then replace the whole works. Parts, about $1,000. Labor is free lol.
So I can tell you for sure that the Barr kit + VP down pipes and hoses, will work, on the starboard side it's a little tight with the steering actuator and the hose coming off the P/S cooler but it all fits and works.

 

[rolmops]

Somewhere in these pages there is a comment made by Bondo about mixing Mercruiser and OMC/ Volvo parts. He does not think that it is a good idea. I would go with Bondo's opinion on anything having to do with engines

 

[Bondo]

Somewhere in these pages there is a comment made by Bondo about mixing Mercruiser and OMC/ Volvo parts. He does not think that it is a good idea. I would go with Bondo's opinion on anything having to do with engines

Ayuh,...... I donno much 'bout the fitment being discussed here,....
But a couple of comments anyway,.. I can hardly believe Lou got the life outa his batwings that he did, after the destruction I saw on other boats, that had those cursed things,....
'n, I seem to remember a difference in diameters 'tween OMC, Volvo, 'n Merc's,.....

 

[Lou C]

I used one set of the Batwings from 2004-2011, at that point one of the 4 outlets was clogging with rust so I replaced them and ran the next set to 2016, at that point, I had the leaky head gasket adventure that resulted in a top engine overhaul (cyl heads, etc). At that point there were no more Batwings to be had, and I researched the conversion. Thought of the dry joint option but there were too many unknowns. So I combined the Barr aftermarket kit with OEM Volvo Penta parts (same as OMC parts but OMC/BRP wasn't selling them any more) and it all fit and worked perfect.
Note the thin walls though compared to the Barr aftermarket....

 

[ccourser]

Thanks for the input I prepped the block ordered some parts and will let you know how it goes.

 

[Lou C]

Here's a few tips, because the clearances on the starboard side are tight, put a little silicone grease inside the rubber hoses (silicone grease doesn't degrade rubber like regular grease) it will make it easier to get it all lined up right.
What I usually do is slide the lower hoses on the Y pipe down to expose the upper edge of the Y pipe, that way I can get the 90* down pipe in place, then pull that lower hose back up. Otherwise, you'll be struggling with it for a while. Port side is easier more clearance.

Also when you get your parts in...
The paint on the Barr units is thin, it will start corroding pretty fast, so brush on a coat of Rustoleum black first. Clean the mating surfaces carefully and measure them for flatness with a straight edge and feeler gauges, should be less than .003". if you have high spots, clean them up with a flat mill bastard file, no rotary tools. Run a thread chaser in the bolt holes for the bolts that hold the elbow to the cyl head, make sure they thread in all the way. Do the same with the holes in the cyl head. I bought 2 longer bolts same thread as the ones for the block and cut the heads off and cut a slot in the end. Thread 2 of these in, slide on your manifold gasket, then the manifold then install the rest of the bolts. Torque them (25 ft lbs) and remove the longer bolts with a screwdriver, and install the last 2 bolts. Same thing can be done when installing the elbows, to keep it all lined up, get 2 longer bolts, and cut the heads off, and cut a slot in the stub. I coated the Barr gaskets with Permatex Aviation sealer (one of their techs advised that) and never had any leaks.

 

[Lou C]

Ayuh,...... I donno much 'bout the fitment being discussed here,....
But a couple of comments anyway,.. I can hardly believe Lou got the life outa his batwings that he did, after the destruction I saw on other boats, that had those cursed things,....
'n, I seem to remember a difference in diameters 'tween OMC, Volvo, 'n Merc's,.....

Here's an old pic when I changed to the last set of Batwings I used, in 6/2011, the ones I took off were on there since 2004, you can see there's no rust in the exhaust ports, the rust on the head is from the gasket holding moisture against it. I guess I got lucky lol. Inboard exhaust to me is always a gamble.
Funny thing though Yamaha 4 stroke OBs have had plenty of trouble with theirs, if not corrected that corrosion will spread over time right up to the bottom of the block. Next symptom, water in the oil.
They actually now have an inspection of the exhaust system listed in their maintenance chart.....

 

[ccourser]

Thanks Lou. Your write up and tutorial has been an inspiration. Going to do a light file on the exhaust manifold surface, overall tolerances look great. Attached is a photo of a dry trial setup. Lou would you mind telling me how tall your exhaust risers are? Attached is a photo of ones I think will work. Be great to know their height before ordering and get the right ones without having to return them for others. Pretty sure I need the ones with 7 degree angles.

 

[Lou C]

Sure thing I will measure them today. If it works out for you then I’ll do the same thing next time I have to change mine which will be at the end of next season for sure….

 

[Lou C]

I think the important thing is actually this:
the total height of the manifold/elbow assembly above the level of the mounting bolt holes in the cyl head, because even if the elbow for the dry joint is the same height as the wet joint, if the manifold height is different where it mounts to the manifold, it throws off trying to determine if it will fit.
to me the critical dimensions are:
total height above the bolt holes in the cyl head
then
location of the center line of the exhaust exit in the elbow, which could be higher or lower than the wet joint
I had all this running in my head when I was thinking of doing the same thing which is why I just went with the wet joint and after 6 years in salt, they are still OK. So, that's not a bad outcome either!

 

[Lou C]

ok did some more thinking on this, there may be 2 dimensions that are important, the one I just mentioned and also, from the 90* down pipes to where the hose for them ends up on the end of the elbow....
I took a pic of a turn key Volvo engine from Michigan Motorz website to illustrate...

 

[ccourser]

Understood it might be tricky. Good point about the manifold bolts. I reached out to Barr, GLM, BPI and other vendors zero responses. Volvo elbows get here Monday so I will trial fit and determine what seems best to order and go from there.

 

[Lou C]

OK the only manufacturer who lists dimensions is GLM. I know there were quality issues with them in the past but this is just informational, so here's dimensions I got for the Merc Dry Joint V6, and the OMC and Volvo wet joint...



The OMC and Volvo are identical...what I get from this is that it appears that the OMC/Volvo elbow is taller than the Merc, but still we would need to know the height of the outlet more than the total height of the casting. Not sure if these will line up, because the difference as measured from the bolt holes is 1 3/8th" taller for OMC/Volvo.
On the manifold, the height from the bolt holes to the top of the manifold sealing surface appears to be close, the Merc is 1/8" taller.
If someone could scale those drawings to full size, it would be easier to tell.
Also another dimension that's important, is looking at it from the front of the engine, how far the manifold sticks out from the block, all of this determines how well the exhaust hoses will line up with the 90* down pipes from the Y pipe.
After a while it made my head spin and I just went with what I know would work. And they have worked fine. If I get 6-7 seasons here in salt water as I have with the first set, that's as good as it gets.