What is this exhaust part?

[80BrownK10]

I know where it goes, it's off my truck. It goes on the manifold between the down pipe and the manifold. Previous owner welded it open. I'm going to cut the deflector out just to get it out of there all together.

But in a factory functioning truck what is it's purpose...I think I maybe have read something on it before but can't remember...is it something to do with cold operation? Partially closing maybe to help warm it up?

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[Catbox]

Yup.
It helps speed up warm up.

 

[legopnuematic]

When cold it is closed, pushing the exhaust through the crossover in the #6/#3 (4/5?) exhaust runner and through the manifold under the carb, and out the drivers help warm the carb up, same premise as an inline engine with the intake and exhaust bolted together underneath the carb.

The factory setup would have a thermally controlled vacuum switch in the intake/water neck to give vacuum to the EFE canister to pull that valve open via a linkage

If going to an aftermarket intake/heads without a crossover no need for it.

 

[bucket]

When cold it is closed, pushing the exhaust through the crossover in the #6/#3 (4/5?) exhaust runner and through the manifold under the carb, and out the drivers help warm the carb up, same premise as an inline engine with the intake and exhaust bolted together underneath the carb.

The factory setup would have a thermally controlled vacuum switch in the intake/water neck to give vacuum to the EFE canister to pull that valve open via a linkage

If going to an aftermarket intake/heads without a crossover no need for it.

To go one step further, older ones would have a thermostatic coil that controlled when they were open or closed. They sometimes would fail in the closed position and then someone would rig them into the open position.

Oh, and they are often called a heat riser.

 

[80BrownK10]

Well I clearly don't need it. It's welded in the open position, has old wire where it was wired open. I have an Edelbrock intake on so no where for the exhaust to route through the manifold.

 

[Goldie Driver]

When cold it is closed, pushing the exhaust through the crossover in the #6/#3 (4/5?) exhaust runner and through the manifold under the carb, and out the drivers help warm the carb up, same premise as an inline engine with the intake and exhaust bolted together underneath the carb.

The factory setup would have a thermally controlled vacuum switch in the intake/water neck to give vacuum to the EFE canister to pull that valve open via a linkage

If going to an aftermarket intake/heads without a crossover no need for it.

And, IMHO, the added back pressure along with the heat from the EGR puts stress on the rings of # 6 & # 8.

Just my .02, but I'd swear my weak ol 350 visibly burns less oil when cold with the vaccuum hose to it disconnected.

Emphasis on visibly ...

I *think* it does warm up faster with it connected, but she is a slow warming beast either way.

 

[Craig 85]

GM calls it a heat riser/EFE valve. Here's what the top side looked like on my '79 K15. My '80 454 was very similar. There was a rod that goes from the vacuum pod down to your part. The one on my '85 is in the second picture.

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[shiftpro]

Duh... it's the power band!

 

[Jimmy84]

GM calls it a heat riser/EFE valve. Here's what the top side looked like on my '79 K15. My '80 454 was very similar. There was a rod that goes from the vacuum pod down to your part. The one on my '85 is in the second picture.

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[Jimmy84]

Will you please send me the part number for the pictured Heat Riser Valve. Trying to find one for my '84 Jimmy.

Thanks

 

[75gmck25]

The older trucks like my '75 use a heat riser valve that is all thermostatic, with no vacuum connection.

Mine was wired open, but the last time I had it off I just ground out the ends of the bolts, filled the holes, and removed the insides completely. I considered removing the whole riser valve, but the fitting on the exhaust manifold was not designed to mate directly to the header pipe (it needed the heat riser in between), and I wasn't sure it would seal properly to the pipe.

 

[Craig 85]

Will you please send me the part number for the pictured Heat Riser Valve. Trying to find one for my '84 Jimmy.

Thanks

I'm not sure this one is correct, but surrounding years appear to use it on various 305 and 350s, but I'm not finding it specifically for a K5. GM 5233150. On another forum the gave the name of Nickson Industries. GM shows 5233150 was replaced by 5234815. Good luck on your search.

1-800-243-0126
Nickson Industries, Inc.
336 Woodford Ave.
Plainville, CT 06062
Tel: 860-747-1671
Fax: 860-747-1678
http://www.nickson.com/newcatalogs/P171-183 Heat Risers, Specialty Items & Hardware.pdf

 

[80BrownK10]

There is also no guarantee that the engine in his k5 is from a k5 originally?

I believe back towards the top of this post someone linked to eBay to OE GM parts for this. Mine is welded open, I didn't but it the flap is still 8n there verticle but like was said 5he manifold is set up to seal to it and I didn't want to have to buy another one without it and then change the pipe on that side so I just put it back in as is.

 

[Octane]

The older trucks like my '75 use a heat riser valve that is all thermostatic, with no vacuum connection.

Mine was wired open, but the last time I had it off I just ground out the ends of the bolts, filled the holes, and removed the insides completely. I considered removing the whole riser valve, but the fitting on the exhaust manifold was not designed to mate directly to the header pipe (it needed the heat riser in between), and I wasn't sure it would seal properly to the pipe.

My old 75 van used to rattle till I fixed that butterfly to stay open.It was heat activated like yours.

 

[Jimmy84]

Craig85: thanks for taking the time to get back to me. Much appreciated.

80brownK10: I have the

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correct manifolds for my year. I have a "Valve Delete" but it's very thick so the studs won't work. I have 3-1/4" studs but They're no quite long enough. It seems the OEM one is thinner.