Exhaust Manifold Question

[Sydmoe]

Hey Guys<br /><br />I am in the process of tearing down my OMC 5.7 I just pulled out of my 1988 25' Invader. Now that I have the engine out of the boat and on the engine stand I can see where the exhaust manifold on the port side has been welded about 6 inches. I am not quite sure why. It must have obviously been cracked and the previous owner had it repaired. Since I am rebuilding the engine should I replace this? Will there be any potential problem if I leave it?<br /><br />Suggestions welcomed.

 

[Trent]

Re: Exhaust Manifold Question

REPLACE IT.........!!!!!!!!!!!<br /> You dont want water intrusion into your engine. Welding them is really not a good thing.

 

[rodbolt]

Re: Exhaust Manifold Question

hello<br /> is this manifold saltwater cooled? if so how old is the manifold? they are cheap compared to the damage they can do if they leak<br />good luck and keep posting

 

[cjflanagan]

Re: Exhaust Manifold Question

<br /><br /> OMC V8 Elbow $105.95

 

[Sydmoe]

Re: Exhaust Manifold Question

The manifold is fresh water cooled....i Started tearoing down th engine tonight. Look like the intake gasket was possibly allowing water to leak into the engine. I least that what it looks like to me......anyone else have a comment??? <br /><br />

<br /><br />Here is the exhaust manifold. Does this weld job look like it will hold out?<br /><br />

 

[dmorley]

Re: Exhaust Manifold Question

Replace the manifold. I agree with you, it looks like water intake to me. Sometimes you can find great buys on this kind of stuff on the internet.

 

[akriverrat]

Re: Exhaust Manifold Question

you had a lot of exhaust leaking at the crossover, center hole. gasket around the water passage looks ok, far left hole. nice and clean in the valley. too clean. is that another crack to the right of the weld? looks like another weld job on bottom right? buy new ones anyway. not worth the risk on rebuilt engine.

 

[Bondo]

Re: Exhaust Manifold Question

I agree with akriverrat......<br />The 1 water passage I can see Looks Fine.....<br />The Exhaust Cross-over ports are a different story.... That's your Direct Path from your Rotten Manifolds, Right to the Base......<br />Looks like if you Replace those Junk Exhaust Manifolds,+ Button it back Up, You'll be Boating Again.....

 

[Sydmoe]

Re: Exhaust Manifold Question

Thanks alot for your opinion guys! I have rebuilt a few car motors back in my teenage years but this is my first marine engine. I will definately replace the exhaust manifold based on your reccomendations. Anyone have any links to some good sources? I checked out ebay but nothing seems to be currently there for my needs.

 

[yoced]

Re: Exhaust Manifold Question

I am not sure about the water in the engine question, but the welds on the manifold are an attempt to fix ICE damage. Those are classic freeze cracks. While it is not usual for a freeze crack in a manifold to cause problems on the inside (ie, leading to water intrusion into the engine), it _too_ common for the same level of care displayed on the manifolds to be evident elsewhere in the care and feeding of that engine.

 

[DJ]

Re: Exhaust Manifold Question

Repalce both manifolds. I wouldn't think of putting on manifolds over one year old on a rebuilt engine.<br /><br />Rerplace the risers too.

 

[Sydmoe]

Re: Exhaust Manifold Question

Consider them replaced!<br /><br />Now, as I have said earlier I have done car motors in a previous life. If I was building one of them and I wanted to get a few extra ponies for a modest price I would probably add headers and new exhaust. What aftermarket manifolds do you guys reccomend or should I just stick with factory replacements?<br /><br />Next question: Where is a good source to buy manifolds and risers for an OMC? <br />(other than the obvious i.e. dealer or ebay)

 

[DJ]

Re: Exhaust Manifold Question

Sydmoe,<br /><br />You are very limited in exhuast choices. You can run headers, yet they have to be water cooled and that gets pricey. Also, I do not know if you want the noise and the hassle of running them out the back of the boat.<br /><br />Osco makes a good aftermareket manifold and riser.

 

[bomar76]

Re: Exhaust Manifold Question

Originally posted by Sydmoe:<br />Consider them replaced!<br /><br />Now, as I have said earlier I have done car motors in a previous life. If I was building one of them and I wanted to get a few extra ponies for a modest price I would probably add headers and new exhaust. What aftermarket manifolds do you guys reccomend or should I just stick with factory replacements?<br /><br />Next question: Where is a good source to buy manifolds and risers for an OMC? <br />(other than the obvious i.e. dealer or ebay)

For an education on GM marine performance mods, buy, borrow or steal the book by the GOD of GM marine engine , Dennis Moore - titled "Small block Chevy Marine Performance" It's $17 or so. Maybe this site sells it somewhere, it's a pretty popular book. Dennis has forgotten more about marine performance than anyone else will ever know.

 

[Bondo]

Re: Exhaust Manifold Question

DJ is quite Right.....<br />You Do have a Few Choices thou......<br />What you took off are known as "Log" manifolds....<br />These are the Worst flowing of the choices...<br />Going to "Center Riser" manifolds will bring a Little better breathing....<br />The Problem with this switch is getting all the plumbing together to match-up to the OMC exhaust run down thru the outdrive....<br />Of course, you Could run them Thru-Hull.....<br /><br />The guy who wrote the book bomar76 mentions, is selling a line of manifolds on ebay.... he's listed as dennismoore16... He's been selling a cast Aluminum center-riser manifold that has cast in runners to smooth the flow..... I don't know if it helps, but it Looks Good on paper....<br /><br />True Headers, Start at about $1000.00,+ Go Up from there.....<br /><br />Has this old 350 got a 4bbl. on it Yet ???

 

[Sydmoe]

Re: Exhaust Manifold Question

Funny you should mention that book by Dennis Moore. I ordered it from Amazon last week and just received it today. I started flipping thru it and your right it seems full of good info and explanations on marine engines and systems. <br /><br />And yes Bondo she has a Rochester spread bore on her. Which I think is giving her enough fuel. Its helping her breathe a little better that I think could make a little difference. Looking through the book by Dennis I see a few diagrams of the Center Riser type manifold you were talking about. From what little I have read it seems like the best prgression from the stock exhaust system without going to the more expensive header type solution. Besides she is just a family cruiser so thru the hull exhaust and is way overboard.<br /><br />If I was to pick up the center riser type manifolds how would one find the nessasary plumbing to hook it into the stock "Y" pipe? I would think this is a common mod for people to want to do and kits would be available. I am either looking in the wrong places or its more of a "your on your own" type project.

 

[Bondo]

Re: Exhaust Manifold Question

If I was to pick up the center riser type manifolds how would one find the nessasary plumbing to hook it into the stock "Y" pipe? I would think this is a common mod for people to want to do and kits would be available. I am either looking in the wrong places or its more of a "your on your own" type project

I haven't seen any Kits, <br />But, the Parts can be found on ebay quite often....<br />Basicly you'll need a couple cast iron Elbows(Not risers, Elbows).....<br />And, a couple lengths of straight pipe to tie it together.....

 

[akriverrat]

Re: Exhaust Manifold Question

here bondo and i disagree. cast iron would be my last choice. fiberglass exhaust parts are readily available for water cooled exhaust. or have a welder fabricate the needed peice out of aluminum. since the al is connected to rest of system with rubber hose electrolysis is not really a problem and a marine alloy will outlast cast iron by years. lighter too. even copper tubing would outlast iron. my experience is mainly with al boats with al manifolds and al through transom pipes. could be i just don't know something that would require the use of 'soon to be rust'.

 

[Bondo]

Re: Exhaust Manifold Question

here bondo and i disagree.

Not Really akriverrat,<br />Sydmoe is looking for the Quick,+ Easy......<br /><br />Personally, My pipes are Handbuilt out of Stainless Steel........(My Hands, of course)

 

[Sydmoe]

Re: Exhaust Manifold Question

And here I thought I was going to be going through this engine rebuild all by my self......I feel like I have a team of experts giving me info and preventing potential mistakes at every turn. <br /><br />Ok, I tracked down Dennis Moore on ebay thanks to Bondos post and I am now leaning towards going to the center riser manifolds that have seperate exhaust gas passages as opposed to the factory log type rear manifolds. Again thanks to Bondos comments and doing some searching I now know that I will have to fab up some plumbing to tie into the existing "Y" pipe. I thought it would have to be some kinda cast iron, aluminum or stainless extention to fill the gap I will be creating. As I searched ebay till midnight for some possible material for the modification I came across a listing for what is decribed as a section of 4" dia fibreglass wet exhaust tubing. Now I see a post from Akriverrat mentioning fibregass as a potential for my plumbing needs. Can this realy be used? Has anyone had experience using this? Should I just use some stainless instead?<br /><br />Again I appreciate everyones help and I am sure it is helping out others following this saga who may be conteplating the same kinda project.