1988 OMC 4.3 l batwing manifold/riser conversion

[frank1492]

My repair guy just erroneously replaced the old 1988 OMC batwing manifold/riser combo units with Mercruiser manifolds and risers. The angles are not correct for connection to the Y on the Cobra intermediate housing. Is there a way to make a connection or will it be necessary to start all over again with the correct OMC conversion kit? Thanks.

 

[Scott Danforth]

Are the manifolds connected to the y-pipe now. If so, dont worry and go boating

Your lucky your batwings lasted this long without hydrolocking your motor

 

[Lou C]

Why not post up pix of what you have so we can see how it looks. There may be a way of making this work with the right parts. The issue I think is that the OMC Y pipe is about 3.5" in diameter while the Merc riser outlets are 4". Thinking back I checked into this a few years back and fount that the later model OMC/Volvo 4.3s used a riser with the same exit size as Merc. They then used an aluminum exhaust pipe that was 4" on the top end and 3.5" on the bottom end by the Y pipe. Take a look at a Volvo parts catalog for 96-98 4.3 exhausts, also look at Crowley marines on line catalog for the 96-98 4.3s. the part is expensive but there is an aftermarket equivalent out there if you goggle the part number...

 

[HT32BSX115]

My repair guy just erroneously replaced the old 1988 OMC batwing manifold/riser combo units with Mercruiser manifolds and risers.

Howdy,

My first question is: Will your "repair-guy" pay for his mistake or did you supply the parts and he just installed them?

 

[Lou C]

http://www.cpperformance.com/p-30084...1986-1990.aspx

This is from a GLM kit, but take a look at the diameter of the hoses from the risers, to the exhaust pipe and then from the pipe to the OMC Y pipe. I could be wrong but I think both the later Volvo and Merc riser outlets were 4" in diameter and the OMC Y pipe is 3.5" just like the outlets on the bat wing manifolds....So post up pix of what you have, and see if if this part with the right hoses will match it up.

http://www.ebay.com/itm/V6-4-3L-EXH...372-/311439942652?hash=item48834463fc&vxp=mtr

 

[frank1492]

Thank you all for your comments but especially to Lou who has clinched it. The mechanic tells me that the Ebay 4" to 3.5" elbow is *exactly* what he needs! Again, Lou, we owe you a debt of gratitude!
I don't feel there will be any need to post a photo.
As to the weaknesses of the batwings, they rusted through 8 seasons ago, the engine hydrolocked and was replaced with new batwings. This time, there was salt water in the engine but it apparently came through the intake manifold. Of course the batwings were replaced on the new block and no more batwings. (You can't get them anyway.)
Wish I could buy Lou a six-pack!
As for having to pay for another manifold/riser kit if this solution hadn't appeared, I offered to split the difference, only because this was an honest mistake made by a single-man business and a truly nice, totally honest guy. Wouldn't you have?
Frank

 

[Bondo]

As for having to pay for another manifold/riser kit if this solution hadn't appeared, I offered to split the difference, only because this was an honest mistake made by a single-man business and a truly nice, totally honest guy. Wouldn't you have?

Ayuh,.... Sure sounds fair to me,.... Yer Mechanic sounds like a Good Friend as well,....

Or a guy ya wanta keep yer good friend,....

 

[Lou C]

No Title

I'm glad this turned out to be the solution, and it appears to work with the Merc manifolds, or the Volvo style ones, which are about the same size, same angle of riser, etc. If you don't mind spending a bit more, it should be possible to use the Merc dry joint system, if their risers are at about the same angle.
BTW, as I said before, I guess I was lucky with my batwings, because with 3 sets used in salt water, each 5-7 seasons each, none ever rusted through, or caused the engine to get water in a cyl. In fact I pulled out one of the sets I have in the garage, and the riser exits still look good, but you never know how thin its getting, where you CAN'T see it......

 

[frank1492]

Right, hard to judge what you can't see. Interesting photo. I bought my 22' Grady Seafarer used in 1998 and the engine hydrolocked and was replaced in 2008. You can do the math. This time the engine didn't hydrolock but lost 3 cylinders due to a leak at the intake manifold, I am told. It could have been repaired, but I opted for a new engine. (You can tell I'm a slow learner to let the batwings get that old.)
What is the Merc dry system? If it means just clamps around the rubber, I think that's what he's doing. He has been doing this for 11 years and has a good reputation.
Thanks for your continued interest.
Frank

 

[Lou C]

google it, what they did was re-do the water path, so the cooling ports are not right next to the exhaust passage, but on either side of it, separated by a lot of area for gaskets. So if there is a leak in the gaskets that seal the water path from the mani to riser, the water can't leak into the center exhaust gas passage, but of course if used to long in salt water they can still rust through. They cost more though. Probably worth it.

 

[bruceb58]

https://www.perfprotech.com/blog/articles/dry-joint-exhaust

 

[Lou C]

Ok as a follow up to this conversation I put together all the parts to do this. I did a top end overhaul on my old 4.3 and no way was I going to take a chance with the old bat wings. So here's what it takes:
2 Barr OMC/Volvo V6 manifolds
2 Barr OMC/Volvo 4" risers

Now here's where it gets a little expensive, you need the Volvo 4" to 3.5" 90* exhaust pipes to mate the 4" hose from the riser to the 3.5" hose at the Y pipe. These parts from Volvo are about $200 each! But it's the only way to do the conversion and not use GLM parts . The only other way I can think of is to use what is called an exhaust "reducer" made by Centek. It is a fiberglass 4"-->3.5" adapter that might work here, but I don't know that for sure. And they are still about 100 each. So there you have it for anyone wanting to this conversion and not use GLM. Of course it cost me more but in salt water cheap exhaust parts are a bad idea....

The Barr stuff looks very good and is made in USA...

 

[Lou C]

PS
I test fitted all the parts today and they fit perfect!
The VP 4"-->3.5" 90* ex pipes match the angle of the Cobra Y pipe perfectly and it looks like a factory installation...

 

[Lou C]

OK I did the installation today and was able to start up the engine after my top end overhaul. It started right up and seemed to run better than it had in a long time, probably due to the better valve sealing of the reman heads I installed.
​Some things I learned:
​The batwings, for all that people like to criticize them are lighter compact and easier to install. I always liked the fact that there is no riser gasket to leak. I know some people had bad luck with these but on a 5/6 year schedule of changing them in salt water, I never had a water in a cyl issue with the batwings.
​OK the Barr stuff is well made and everything lines up like it should. The Volvo Penta OE hoses are interesting, they have a few little pictograms that tell you how to orient the hoses. On one end of the 4" riser hose there is a little icon that symbolizes water , looks like this ~~~~ that end goes over the riser and then snaps in place, inside the hose there is a locating ring that fits into a groove in the riser. The other end of this hose has another icon that looks a bit like the 90* adapter that adapts the 4" hose to the 3.5" Y pipe. On the lower hose that connects to the bottom of this adaptor, same icon so you know which end of that smaller hose goes into the adaptor. It all slides together well.

​A few tips that I picked up on this job, keep in mind the only marine exhaust I ever did was the batwings and they were really simple to install.

​Pick up a thread chaser and make sure to chase the bolt holes in the cyl head and in the manifold.
​I like to test fit the bolts to make sure they will tighten all the way down. Get all the paint off the sealing surfaces and clean them REALLY well.
​To mount up the manifolds, its easier if you get two longer bolts, cut off the heads and grind a screwdriver slot in the end where the head was. These you can thread in to the front and rear holes in the head, then slip gasket and the manifold on. Next get the bolts started, lift up the manifold a bit so that the bolts will more easily align with the threads in the head. After you install all but the front and rear bolts, remove the longer headless bolts and then install the last 2. I put Permatex Aviation Sealer form a gasket on the threads of all the bolts and on the Barr riser gaskets are per their tech guy's instructions.
​I warmed up the engine and then re-torqued all the bolts with my clicker torque wrench. It was a bit pricey (a lot more than the GLM stuff, but shops here have such bad experiences with GLM exhaust they will not order it), but fits and looks great.

 

[HT32BSX115]

Nice Job Lou! :thumb:

 

[Lou C]

https://www.dropbox.com/s/55j6h4dd1u8fv0k/IMG_2273.MOV?dl=0

​Here she is up and running with the new center riser exhaust....

 

[nutnboltguy]

i realize this is a thread from 2017 and there are rules n such about reviving old posts, but i think this pertains to what's being talked about here and i have a question for you Lou C .

i pulled my engine (88 OMC 4.3) to address an oil leak that was dirtying up my bilge. upon inspection both of my batwings were cracked. obviously im going to replace them with new manifolds and im looking at the GLM's since they're available and within my budget. i like good stuff and if i had another $800 to spare id go for the Barr setup, but again, im not cash rich right now and want to get back out on the water asap and finish out the season without hydro-locking my freshly rebuild motor with less than 200 hours on it.

you previously mentioned your shop wont carry the GLM's due to your salt water environment, so i get it about cheaper metal castings not lasting in salt. im in Northern California and i only run my boat in mountain runoff fed freshwater lakes. my question is; do you think the GLM would be a good budget solution and last several seasons in the freshwater im in versus the saltwater you're running in?

 

[jbcurt00]

i realize this is a thread from 2017 and there are rules n such about reviving old posts

Yes, yes there are

Closed