cobra exhaust manifolds

Lou C

Lou C

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Nov 10, 2002
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11,831
Re: cobra exhaust manifolds

I have a 4.3 that uses the hard to find one piece design. I got some when they were available, and got an extra set for the future. Now my take on conversions is there has to be a good reason to do it, because there can be unknowns along the way. I had heard of people doing conversions, but I also knew if I could get the OE ones, it was plug n play with no worries. SO, if you can get the original OE, or aftermarket, I'd stick with that, because converting will require new hoses, elbows, etc and will add up money wise. I don't know if you will see better power with the center riser. Go over to www.dougrussell.com and look in the OMC parts section, and look at years up to 90 or so, that is your style, then 91 and after is the newer style, and add up the cost of all the parts you need to use center riser manifolds. I found it was more expensive, when my one piece ones cost close to 400 or so a side, to convert to the center riser, but subsequent replacements would of course be cheaper since you could use aftermarket stuff for the manifolds and risers. Why don't you contact Marine Manifolds in Farmingdale, they may know for sure what is involved.
 
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HT32BSX115

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Dec 8, 2005
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10,083
Re: cobra exhaust manifolds

I'm with Lou on this. I would check with Doug Russell and the other OMC types. I would also try to find a dealer that might have some experienced people that might have already done this. <br /><br /><br />Give this thread a little while. I'll Bet Don S. In KTN AK will probably have already seen a "been there-done that" mod too and will have an opinion.(we're lucky to have people here like that with experience in this stuff!)<br /><br /><br />I also have a small crack in at the bottom of my right side manifold just forward of the rear cap.<br /><br />I have had very good luck with brazing cast iron manifolds in the past so I am going to try that. The hairline crack is in a non-structural area at the bottom. I did drain them but evidently there was a little bit of residual water in them after draining or jostling the boat around allowed some water to end up in there.<br /><br />Next winter I am going to fill the whole thing with Anti-Freeze!<br /><br /><br />Regards, <br /><br /><br />Rick
 
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whywhyzed

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Re: cobra exhaust manifolds

I watched eBay for 2 years... recently found an NOS set for my 3.8 OMC (the rear exit type with risers) new in the original crate. Approx. 1/3 the price I was quoted for new ones a couple years back. It's a pain to keep searching, but search time seems to be the required investment for finding NOS. They're sitting in back parts rooms somewhere... it's just finding them...
 
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whywhyzed

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Re: cobra exhaust manifolds

Oh - I just read the other thread- I think the rear exit type are still avail. for chevy V8 <br />I don't think conversion to centre riser would make any noticeable HP gain. Maybe 2 or 3 HP... the rear exit are not exactly restrictive....the centre mixing of exhaust pulses helps a 500HP small block, but for 230HP I doubt it matters...
 
Scaaty

Scaaty

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Re: cobra exhaust manifolds

Originally posted by HT32BSX115:<br /> I have had very good luck with brazing cast iron manifolds Rick
Click to expand...
In case you don't know, that's about all you CAN do with cast iron...
 
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HT32BSX115

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Re: cobra exhaust manifolds

Well you're right, for most of us! It's possible to weld cast iron. You really need to have a furnace to heat the casting first (I don't have one)....You can also weld using GTAW(Some used to call it TIG...I've got one of those!) but the rod is pretty expensive....In Fact it's VERY expensive! When i priced it, it was about the same as a new manifold! Makes it not worth it. Brazing works very well. I've done a few over the years and haven't had one crack yet. (It's luck though!....they ARE likely to crack!)<br /><br /><br />Regards, <br /><br />Rick<br /><br /><br />
Originally posted by SCAATY:<br />
Originally posted by HT32BSX115:<br /> I have had very good luck with brazing cast iron manifolds Rick
Click to expand...
In case you don't know, that's about all you CAN do with cast iron...
Click to expand...
 
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HT32BSX115

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10,083
Re: cobra exhaust manifolds

You're right it is a REAL pain! I saw 2 NOS manifolds for a 7.5L OMC for sale and I just shined them on! "why would I want them?".....(now I want them!)<br /><br /><br />I regularly do an OMC search on Ebay motors for any and everything!<br /><br /><br />
Originally posted by hystat:<br /> Oh - I just read the other thread- I think the rear exit type are still avail. for chevy V8 <br />I don't think conversion to centre riser would make any noticeable HP gain. Maybe 2 or 3 HP... the rear exit are not exactly restrictive....the centre mixing of exhaust pulses helps a 500HP small block, but for 230HP I doubt it matters...
Click to expand...
 
B

boatgrunt

Petty Officer 1st Class
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Aug 28, 2005
Messages
285
Re: cobra exhaust manifolds

Hi - First, I am not a mechanic...just a first time boat owner/do it yourselfer.<br /><br />That being said, I have converted my 89 4.3 Cobra 1-piece exhaust manifolds to the center-rise/elbow exhaust manifolds. The fit was not a problem, however, I have not run my motor with the new manifolds. Tashasdaddy, a poster to this site, converted from 1-piece to 2-piece exhaust manifolds but ran into trouble with his Vortec engine and the 3" risers. I think he had to go to the 4" risers in the end. <br /><br />I agree with the others...if you want the safest route, go with the 1-piece. If you want to try and save some money and time, talk to your local marine technician and see if the conversion to the center risers/elbow package might work for your engine.
 
KaGee

KaGee

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Re: cobra exhaust manifolds

GLM is offering replacement manifolds for just about all of the OMC's... The batwing version should be available by spring if not now.
 
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lakelivin

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Aug 19, 2004
Messages
1,172
Re: cobra exhaust manifolds

Originally posted by KaGee:<br /> GLM is offering replacement manifolds for just about all of the OMC's... The batwing version should be available by spring if not now.
Click to expand...
No sarcasm or disrespect intended, but haven't they been saying that for over a year-and-a-half (i.e., weren't they saying in fall of 2004 that they would be available in spring 2005)? <br /><br />Any new info that would indicate they're really gonna be available shortly?
 
KaGee

KaGee

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Re: cobra exhaust manifolds

I don't know what the problem was or is Lake.<br />They have to be bombarded with requests for that and the Mercruiser batwing as well.
 
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rojoc

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Aug 15, 2005
Messages
103
Re: cobra exhaust manifolds

I don't have issues with the existing exhaust manifolds (least not that I am aware of), but 450 hrs. and 18 years I am assuming that the manifolds should be changed. I ALWAYS flush with fresh water after a days outing.(on a trailer).After some research online I see log type manifolds are available so I will stay with what I have. Thanks again to all.
 
tashasdaddy

tashasdaddy

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Re: cobra exhaust manifolds

i got it straight from GLM on monday, that there will be a "delay" in the batwings. they don't know how long, had a problem in production is all they would say.. HGE is suppose to have a conversion kit, coming out in 2 weeks. Peter Wong at that company in Canada, can't remember name right now, sent me pictures of they new line. can email to someone if they want to post it. <tashasdaddy@comcast.net>
 
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DHPMARINE

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Dec 16, 2003
Messages
3,688
Re: cobra exhaust manifolds

Last November at the Kellogg Marine Dealer meeting in Conn.the Osco rep assured me they would have OMC Cobra V6 manifolds soon (last spring).About the same time I called Barr.Not too promising.Why should they tool up to build manifolds for engines that old,is what I was told.<br /><br />I'm not trying to dump on anyone,but as we wait,the engines get older and I wonder if we'll see a direct replacement for 984221/984222.<br /><br />So maybe adapt as best we can (safely) and stop waiting ?<br /><br />DHP
 
KaGee

KaGee

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7,069
Re: cobra exhaust manifolds

I used the OSCO adaption from the rear riser OEM to a center rise configuration for my '82 3.8L V6. <br /><br />
New%20Manifold.jpg
<br /><br />
New%20Manifold%203.jpg
 
R

rojoc

Petty Officer 2nd Class
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Aug 15, 2005
Messages
103
Re: cobra exhaust manifolds

KaGee: Nice looking set-up. Well done!
 
R

rojoc

Petty Officer 2nd Class
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Aug 15, 2005
Messages
103
Re: cobra exhaust manifolds

KaGee: How did you post the pictures?
 
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