welding cast exhaust manifold


Old 04-29-04, 11:06 AM
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welding cast exhaust manifold

I'm work'n on an exhaust, and I have to remove a small block that's part of an emissions setup. The emissions is no longer going to be used on this vehicle. From what I can see it's about a 2" block.

Without removing and installing a completely new exhaust setup, I have 2 options, I can make a filler pipe, or I can weld closed the block and drill out the center.

The block in question has a butterfly mechanism in it that opens and closes to let exhaust gases out only at a certain point. It has a rod coming out of it that's attached to a vacuum canister up higher on the engine. The block is right after the manifolds, but before the catalatyc converter (sp?)

The block appears to be cast, it has the same rusty burnt look the manifolds have, plus coming right off the manifolds, it needs to be able to stand up to some heat, right?

If I choose to go to a filler pipe, would 1/4" wall thickness be enough to stand up to the heat coming out the manifolds?

If I choose to weld closed the hole where the rod is hooked up, what material can I use for a filler plate?

I've never welded any cast, but from what I've read, I can do it simply with an acetylene torch, provided I preheat it cherry red, weld while it's hot, heat it again when I'm done, and then allow it to cool slowly. I also understand I would need a special welding rod.

I have access to most forms of welding at school, but I would prefer to do this at home because it would be quicker. I have access to an acetylene setup, a MIG, and a 110 flux core. I doubt the MIG or flux core could be used to weld cast from what I've read.

Can someone give me some advice here?

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Old 04-29-04, 11:46 AM
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Hello: Mathius

The part you call a butterfly mechanism pertains to the engines preheating system. The butterfly valve inside it opens and closes based on engine initial cold temperature startup.

When the baffle is closed, it recirculates some of the hot air to the intake and may also recirculate some of the exhaust gases back into the engine. Different setups are used but the purpose(s) remain the same.

Faster prewarm up upon cold starting and in some types, diverts warm heat from the manifold to the air intake. When engine warms up to a certain point, baffle begins to open. Once temp reached, opens fully.

You may want to reconsider total removal of that device and or any alteration(s) to it when not sure how it will effect the engines prewarm up.

Check with a mechanic before altering, modifing or removing that device.

As to the aspects of welding, best left to the professional moderators in the forum. Whom will assuredly be able to help you additionally.....

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If you live in state which checks smog systems, any modifications, alertations, etc to that device will fail the smog test b4 the test is even started...

Unless the vehicle is excluded, by year of manufacture, from smog checks...in your specific state.
Old 04-29-04, 08:23 PM
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Are you building a daily driver or a hot rod?


The piece you are referring to is called the heat riser valve.
It is a very simple device as Sharp Advice says that blocks the flow in the exhaust to force hot air through the intake manifold to warm up the manifold and carb or tbi.
It is operated by vacuum through a vacuum valve that senses intake manifold temperature.
Why I'm telling you this is that if you leave it or make it work properly your engine will warm up much quicker.

If you are determined to eliminate it the simplest way would be to drill or grind out the shaft for the damper, thread the holes and install a bolt in each opening.
Old 04-29-04, 09:05 PM
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Emissions is not an issue, this car is far too old to have emissions testing in my county, or any of the surrounding counties.

I am determined to remove it. The bracket the vacuum is attached to is impeding the installation of taller valve covers. I have thought of making a new bracket, but then I'd have to figure out how to re-work the rod so it still works. Also, I want to go as simple as possible with this car. I've already pipe pluged the tvs, removed the EGR and blocked it off with a stainless plate, and installed a new waterneck. All emissions will be going except the fuel canister because it doesn't hurt performance and it will help deal with fumes. I'll probably actually replace it with one that has a replaceable filter element.

Anyways, back to the question at hand. Greg, I would still have to weld the butterfly opened, would I not? If not then at least install a block where the butterfly is. This seems to be a common modification from what I've been reading, and I've heard of people welding it easily, so mayhaps it isn't cast?

Old 04-30-04, 05:05 AM
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Hello: Mathius

Inside the valve, on the shaft, the butterfly plate whould be either screwed onto the shaft or spot welded to it. In the case of spot welded, a chisel and hammer, a few well placed hits, knocks it off.

Once that is done, reassembly can be done. Now it makes no difference which way the shaft is positioned. The tube or pipe or whatever than is in the way for the new valve covers can be removed. Hole plugged.

In the above, there than should only be one place in the valve to block off and the other end going to the intake manifold or carb can be blocked off. Keep in mind the air volume to the manifold or carb, whichever is also decreased by this amount.

The point is to make the operation the heat riser valve inoperative, in the simplist way possible as you stated, but still remain there. Less work and still obtaining the final results. Or simply weld the counter weight (when the internal plate is in the open position)

Based on the smog equipment you stated the vehicle has, in my opinion and based on prior experience and testing, while working in the industry back in that era, removal of the EGR, PCV, tvc, etc smog systems, the engine may seem to run better at first or appear to. But not very well for very long.

Properly operating smog systems, based upon all the factory testing data accumulated by the "Big 4" auto makers, under all possible conditions, smog systems actually improved engine breathing, perfomance, fuel economy and internal cleanliness, etc.

I was fortunate as a result of working in that area, the testing facilities and labs of the industry and being a field rep mechanic for one of the BIG 4. The smog laws may not apply any longer but the engine does not know that.

Keeping in mind, the engine was designed and built to operate with all smog systems in proper working order. There is much more than devices and equipment, at work on the engine, than meets the eye.

And for very good reasons. Of which I was not aware of either, until being exposed to the labs, testing and racing conditions, prior to mass production.

Do as you must and will.
Good Luck
Old 05-02-04, 08:14 AM
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A cast iron exhaust manifold can be either brazed or welded with oxy/acy. It seems the simplest solution would be to cut a plug ( 1/4" mild steel is fine) and braze it in place.
Old 05-09-04, 03:47 PM
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Like Greg said, thread it and stick a bolt ofr plug in it. I have welded them shut also (engines for equipment) and any process that plugs the hole would be fine. I am also in a certain agreement with Sharp, you could be creating some other problems without correction, the main one is pre-ignition from removal of egr. That may be overcome by using premium fuel. PVC should always be left on. About the only one I get rid of on occasion anymore is the air injection. Big HP robbing useless deal on SOME engines. My pickup truck certainly benifitted from removal of that during a rebuild. I had to have it for ideler so I took the vanes out. I have heard of as much as 20HP under certain occasions and when I got it back on the road it took some getting used to as at above 65 mph it seemed to want to work hard, now it has some power in that range. (easy to speed) Only 300 6 cid in a F250 4x4 so it wasnt over powered to start with, but that helped.
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Old 02-20-05, 08:16 PM
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That valve pre-heats the intake manifold as mentioned above. Without it, you will suffer hesitation, & maybe even stalling because the fuel will not stay atomized in a cold intake manifold & condense & form droplets. You'll always wonder why it stalls pulling away from the stoplight.
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