Replacing batwing manifold questions (and other questions)

[Payne]

Some complications: '91 omc cobra drive, but a 2008 4.3 Vortec engine. Cracked block, probably caused from a cracked batwing exhaust manifold.
I guess I will get a remanufactured Vortec long block and transfer the water pump, starter, flywheel, alternator, etc. from the old engine.
Questions:
Are there any significant differences between the Vortec engines through the years I need to know about before I get started?

There seems to be a bunch of different riser heights that are listed as replacements for the batwings. How do I figure out which to order?

A local mechanic suggested that the current 4 bbl intake could be cracked as well. Besides less power, is there any downside to converting to a 2 bbl instead?

Any recommendations for a place to order a good long block on a budget? Suppliers to stay away from?

Thanks in advance

 

[Lou C]

The question is why did the block crack? A rusted or cracked manifold would cause water ingestion not necessarily a cracked block. If your 2008 Vortec was a marine block then replacing it with the same thing should allow you to use all of your accessories. The intake can be checked by a machine shop for cracks. If you were to convert to a 2bbl you will need a new 2 bbl carb to go with it, personally I’d stick to the 4bbl having had one myself. I have done the batwing to 2 piece exhaust conversion. I used Barr aftermarket OMC/Volvo manifolds & elbows and V/P exhaust pipes that connect from the elbow outlet to the Y pipe. I used the standard height elbows and they work fine on my boat; I measured the tops of the elbows as 15-16” above the static water line. V/P does make a taller elbow/riser if needed. The Barr exhaust is reasonable in cost (~~$725 or so), the V/P parts are expensive (each exhaust pipe is approx $225 if new) these can be bought used or GLM makes an aftermarket version. I’ve posted up pix if you do a search....

 

[Payne]

The question is why did the block crack? A rusted or cracked manifold would cause water ingestion not necessarily a cracked block. If your 2008 Vortec was a marine block then replacing it with the same thing should allow you to use all of your accessories. The intake can be checked by a machine shop for cracks. If you were to convert to a 2bbl you will need a new 2 bbl carb to go with it, personally I’d stick to the 4bbl having had one myself. I haYou know, I just assumed that the ve done the batwing to 2 piece exhaust conversion. I used Barr aftermarket OMC/Volvo manifolds & elbows and V/P exhaust pipes that connect from the elbow outlet to the Y pipe. I used the standard height elbows and they work fine on my boat; I measured the tops of the elbows as 15-16” above the static water line. V/P does make a taller elbow/riser if needed. The Barr exhaust is reasonable in cost (~~$725 or so), the V/P parts are expensive (each exhaust pipe is approx $225 if new) these can be bought used or GLM makes an aftermarket version. I’ve posted up pix if you do a search....

You know, I just assumed that the block was cracked because of the the "freeze" plugs were pushed out. The oil was emulsified so water intrusion was there before I drained the block for the winter.

Staying with the 4bbl would be the easiest and cheapest option, especially if the manifold isn't cracked. If it is cracked I would need a new manifold anyway and I didn't feel I needed the extra power. But, you are probably right.

Thanks on the advise on the exhaust conversion. I'll check the heights to see as you did to be sure of the height. I had forgotten about the exhaust pipes; thanks for the reminder. I'll check out your pix, too.

Payne

 

[Payne]

After reading your post with the pix, I see that the parts are Volvo. Are they the same as the OMC? When looking at a long block, do I have to use one that is listed as OMC or will the Volvo be identical? Pardon my ignorance.

 

[Lou C]

The parts are identical same part numbers etc. Remember OMC and Volvo had a joint venture from 1994-1998 and Volvo actually used a lot of OMC parts, like the exhaust, the thermostat housing, power steering coolers etc. The exhaust parts are no longer sold by OMC but they are sold by Volvo Penta.
The long blocks are all standard GM 4.3s, the ones you want are set up for marine/industrial use, using a late model one from a GM truck is going to be more difficult due to changes made over time. All the I/O companies took the basic GM marine/industrial block and added their own accessories to it like exhaust, shift linkages, and marine specific starters, alternators, distributors and carburetors. The main differences for marine use are stainless steel head gaskets and brass freeze plugs. Normal head gaskets and freeze plugs will corrode if used in raw water cooling applications so this is a must for marine use unless you use a closed cooling system.
I would stick with the 4bbl carb especially if your carb is good. I see no point in going to less power with a 2bbl. Remember if the intake is cracked and you want to go to a 2bbl set up you have to buy an intake AND a carb. Can't put a 4bbl carb on a 2 bbl manifold!
Post up pix of your engine for more specific advice and ping Scott Danforth because he knows about all the different changes made in the 4.3s over the years they used them, there are a LOT.
In my '88 I am still running the original engine which is the pre-vortec (12 bolts for the intake manifold), one piece main rear seal, non-balance shaft, but with roller camshaft. I changed the heads 3 years ago but other than that and normal maintenance (in salt water we have to change the exhaust every 5-7 years) the engine is original. I changed the original batwings in 2004, then again in 2011, and in 2017 when I replaced the cylinder heads I changed it over to the 2 piece exhaust set up just like what Volvo used on all the 4.3s before the cat converter exhaust.

You could have had a failed manifold but if a freeze plug pushed out that's incorrect or no winterizing. Failed exhaust manifolds don't do that, they put water in cylinders and rust up exhaust valves and cylinder walls.

 

[Lou C]

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see parts #s 10-14, those are the hoses, clamps and exhaust pipes
if you use a Vortec engine the one way check valves that prevent vacuum in the exhaust from pulling water up the exhaust are recommended (part #s 27, 28, 29) the pre-Vortecs don't need these, because the cam profile on the Vortec engines was more aggressive to put out more power and they are more prone to pulling water up the exhaust. So you can see that after the Vortec engines came out these one way check valves were added to the exhaust elbows. If a vacuum develops in the exhaust it allows air in to 'break' the vacuum to keep water from coming up the exhaust (this is called exhaust reversion)...I didn't have to add these to mine because mine is a pre-Vortec but if I replaced it with a Vortec then I would add them.

PS I've had the Volvo exhaust on now for 3 years (Barr exhaust manifolds & elbows & gaskets) and it functions perfect, no leaks, everything fit like factory. The Volvo stuff is expensive though, you might be able to find the exhaust pipes used (ebay, etc, if used in fresh water). I know that GLM made a copy of these but the shape is a bit different and there may be clearance issues with the power steering hoses on the starboard side.

 

[Scott Danforth]

some light reading on the 4.3.

complete history of the 4.3 liter with casting numbers

thought I would post the complete history of the 4.3 liter that I could find. These are links and articles that I have bookmarked for my own use, however they should help many people. it may help some people when looking for parts or sourcing a salvage yard motor or a reman. keep in mind that...

forums.iboats.com

your 1991 motor was a 1988-1991/92 vintage only.
your 2008 motor would be a 2007 and later 4.3

4.3families are
1985 only (2-piece RMS seal)
1986
1987-1988
1988-1992
1993-1995
1996-2006
2007-2011
2013-2014
2015-today

yes, there are many many many changes over the years.

 

[Payne]

Thanks for the education, guys. I'll start tearing it apart and see what really happened and go from there. I'll post pix when I get the heads off.

 

[Payne]

Alright, I had an aftermarket OSCO CSCR643 manifold and the OMC risers installed when I replaced the engine. (by the way, it is a 2006, not a 2008). These manifolds were discontinued long ago, but I found a note on an old catalog that says these are not to be used with Vortec engines, which is what I had. Something about back pressure problems. This may have caused the failure of the Votec replacement engine.

I can't seem to find any manifold/risers that say specifically that either they will match up with the existing OMC y-tube setup AND say they will work with Vortec engines.

I can find kits that "replace the batwing" manifolds, but say used for years 88-90. This would fit the existing exhaust, but I don't know about the Vortec application.

Exhaust manifold GLM58995 kit is listed as a replacement and looks like a different design, but I'm not sure that it solves the Vortec engine problem: it doesn't say one way or another. Similar risers for a OMC one piece replacements have provisions for a Volvo Penta anti-siphon valve or not. It looks like same risers, but one is drilled and tapped for installation of the valve.

So there in my dilemma. Buy the GLM kit for the new replacement engine that may not work with the Vortec, buy the valve and try to figure out how to fit it into the kit riser, or buy the riser that has the valve in it and throw away the one that the kit came with. The Volvo shows the manifold and valve riser (at about twice the price), but doesn't include the 90 degree down turn and reduction to fit the existing OMC exhaust.

Any ideas, or am I screwed?

Thanks, Kirk

 

[Lou C]

OK the OSCO conversion probably didn't allow for the fact that the Vortec engines due to the camshaft timing developed more vaccum in the exhaust system and would pull water up the exhaust (exhaust reversion). What Volvo did when they switched to the Vortec engines was change the shape of the 90* aluminum 4" to 3.5" adapter pipes that fit between the rubber hoses on the exhaust elbows and the Y pipe. And they added vacuum check valves in the exhaust elbows to allow air IN, if vacuum developed in the exhaust, but no exhaust could escape OUT (one way check valve). I used the updated 4" to 3.5" aluminum adapter pipes on mine, but did not need the check valves because I still have a pre-vortec engine, no issues with exhaust reversion. If you use the Barr aftermarket exhaust kit for the OMC/Volvo design exhaust I believe they are tapped so you can install those one way check valves. Sounds like that's the way to solve your problem. You can't go wrong using the same exact set up Volvo used when they were selling these engines and the Vortec V6s were used for a long time with this same exact exhaust. See the link to the Volvo catalog I posted up above.
If I repower mine with a Vortec V6 then I can keep the same exhaust just add the check valves.

 

[Payne]

OK the OSCO conversion probably didn't allow for the fact that the Vortec engines due to the camshaft timing developed more vaccum in the exhaust system and would pull water up the exhaust (exhaust reversion). What Volvo did when they switched to the Vortec engines was change the shape of the 90* aluminum 4" to 3.5" adapter pipes that fit between the rubber hoses on the exhaust elbows and the Y pipe. And they added vacuum check valves in the exhaust elbows to allow air IN, if vacuum developed in the exhaust, but no exhaust could escape OUT (one way check valve). I used the updated 4" to 3.5" aluminum adapter pipes on mine, but did not need the check valves because I still have a pre-vortec engine, no issues with exhaust reversion. If you use the Barr aftermarket exhaust kit for the OMC/Volvo design exhaust I believe they are tapped so you can install those one way check valves. Sounds like that's the way to solve your problem. You can't go wrong using the same exact set up Volvo used when they were selling these engines and the Vortec V6s were used for a long time with this same exact exhaust. See the link to the Volvo catalog I posted up above.
If I repower mine with a Vortec V6 then I can keep the same exhaust just add the check valves.

Thanks for the information. But the Volvo risers with the check valve are about $160 apiece. Plus the $900 for the manifold, 90 degree piece to make connection to the OMC exhaust. I was hoping that someone knew for sure if the check valve was not needed as a parts guy on the phone told me. I appreciate the info, though.

Kirk

 

[Lou C]

You don't have to use Volvo parts for manifolds and elbows, get the Barr kit it is just as good and you can use the same fittings for the check valve. The only OE Volvo parts I would use are the check valves and the 90* exhaust pipes.

 

[Payne]

You don't have to use Volvo parts for manifolds and elbows, get the Barr kit it is just as good and you can use the same fittings for the check valve. The only OE Volvo parts I would use are the check valves and the 90* exhaust pipes.

Ok, thanks. I didn't see that the Volvo valves could be installed in them. Sorry for my ignorance.

 

[Lou C]

No worries, Volvo charges a premium price for their parts and my goal was always to get the best parts without getting robbed by either OMC/BRP or Volvo. So when I did my exhaust conversion I used the Barr aftermarket exhaust and Volvo 90* exhaust adapter hoses and aluminum exhaust pipes. I knew that GLM makes an aftermarket copy but I didn't think the quality or design was as good, but if you look on ebay you can find those Volvo parts used in good shape. Same thing with starters & alternators (I used ARCO) mechanical fuel pumps (I use Carter or Sierra) and carb rebuild kits (I use Cliff's High Performance Quadrajets, or a standard Holley kit if its a Holley 4bbl).

 

[Payne]

No worries, Volvo charges a premium price for their parts and my goal was always to get the best parts without getting robbed by either OMC/BRP or Volvo. So when I did my exhaust conversion I used the Barr aftermarket exhaust and Volvo 90* exhaust adapter hoses and aluminum exhaust pipes. I knew that GLM makes an aftermarket copy but I didn't think the quality or design was as good, but if you look on ebay you can find those Volvo parts used in good shape. Same thing with starters & alternators (I used ARCO) mechanical fuel pumps (I use Carter or Sierra) and carb rebuild kits (I use Cliff's High Performance Quadrajets, or a standard Holley kit if its a Holley 4bbl).

Ordered the Barr kit. Thanks for your help and advice.

 

[Lou C]

Sure thing. If you want the paint to last:
after removing the paint from the sealing surfaces of the manifolds and elbows (where the gasket goes) paint the with Rustolieum black with a brush much less messy than spray and that paint will last with no rust the next season. The thin coat of spray most manifold companies put on just does not last.

 

[Payne]

Sure thing. If you want the paint to last:
after removing the paint from the sealing surfaces of the manifolds and elbows (where the gasket goes) paint the with Rustolieum black with a brush much less messy than spray and that paint will last with no rust the next season. The thin coat of spray most manifold companies put on just does not last.

Sounds good.

 

[Lou C]

see the plug with the hex recess, that's where the vacuum break valves go....