What is this?

[HotRodScottsdale]

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What is this And what dose it do? It's on a 76 with a 350 small block straight piped
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[HotRodScottsdale]

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[RandyP]

Was part of the emissions that were removed.

[HotRodScottsdale]

Should it be flipped any certain way? It's flipped up right now, dose that effect anything? What dose it do inside the pipe?
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[jame]

Its the heat riser. It has a butterfly inside that when cold channels warm air through a flexable pipe to the air cleaner. The heat shield has a hole in the top you can see that the pipe would have attached too.

[RandyP]

Had a K5 that had it on there. I took the exhaust loose and removed the piece and blew the butterfly out with a torch and then put the piece back on. They sell a replacement section at the auto parts stores but the blow torch method was free.

[motornut]

here is a close pic
mine fell off the 79 after i took the bolts out lol

I've seen holes drilled/filled to see if it was open or closed before,poke a coat hanger up,holding open tacked from outside

[East End K5]

I have the same thing, I removed the valve and thingamabobber that tied into the vacuum line with the carb and bypassed it. I assumed it was part of the A.I.R. (smog) system on my 454. I plan on pulling it all the way out when I do new exhaust. I was thinking it had something to do with the choke as well since it was tied into the carb... I get a kick out of early emissions attempts..

[Phillip Pennartz]

That is the heat riser. yours was operated with a vacuum diaphragm. Some earlier ones had a bimetallic spring. Anyway this heat riser when closed forced the exhaust up thru a port in the middle of the exhaust manifold and then thru a passage under the intake manifold exiting thru the other exhaust manifold.
When this is operating right is not a bad thing to have. It helps the motor to warm up faster which helps mileage, emissions and the heater.
The sheet metal part riveted to the middle of the exhaust manifold is the heat stove. When the engine is cold, warm air from around the exhaust manifold is pulled into carb to help with fuel vaporization . Not a bad thing to have either. It helps with cold weather drivable and emissions. When motor is warm this isn't used.

[HotRodScottsdale]

It's a summer truck, never seen snow and No plans too so would it be smart to take out?
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[RandyP]

Since the only thing left is the butterfly piece, there is no sense in leaving it in there. Now if you are wanting to spend a few $100 and buy all the junky emission pieces that have already been removed from your truck and try to make the valve work again, then leave it.

It is probably not hurting anything, but it has zero function right now.

[motornut]

for a summer truck you won't miss it
around here most seem to rust and sieze up,in a bad way, closed
looks a little cleaner I think too

[paintslinga2010]

I'm dealing with the same part. Mine is all still intact except i removed the vacuum line. Is it now stuck open or does it need to be wired open?

[425HP409]

As Philiip Pennarz stated correctly, this is a "Heat Riser Valve". As it is the open position at this time from the photo you posted, there would be no real value in removing it. If it were to stay in the closed position you would have an exhaust restriction for the right bank. Unless it is rusted stuck, it can be moved by the lever on it. If it is in the closed position and you cannot move it, it would be a good thing to take the exhaust loose and remove wither the flapper valve, or to replace the assembly with a "Dummy Valve" available from the parts store.

[Mrknowitall]

Another simplistic 70s idea

Lol but really smog requires it to b installed, it was used to heat the engine faster to reduce emmissions upon first startup.

Take an oxy torch to the mechanism if u wanna keep the look without the restriction. But beware here n cali all smog must be retained, hwy patrol can pop ur hood and fine u if alls not there so keep in mind!
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