vacuum valve on driver's exhaust manifold outlet?

[WebMonkey]

google didn't answer my question so i'll ask here:


sorry i didn't take a picture.

crawling under the 1985 k20 to trace a 'line', i found it attached to a vacuum operated valve at the end of the driver's side exhaust manifold. it is right at the junction of the exhaust pipe going back to the muffler.

the 'line' from the valve is unterminated right by/below the air filter housing.

what is this for?

exhaust gas restriction of some kind?

thanks for your time.

 

[Turbo4whl]

google didn't answer my question so i'll ask here:


sorry i didn't take a picture.

crawling under the 1985 k20 to trace a 'line', i found it attached to a vacuum operated valve at the end of the driver's side exhaust manifold. it is right at the junction of the exhaust pipe going back to the muffler.

the 'line' from the valve is unterminated right by/below the air filter housing.

what is this for?

exhaust gas restriction of some kind?

thanks for your time.

No, that is your hear riser valve. When the engine is cold it shuts down some of the exhaust, forcing that heated exhaust back through the intake manifold right under the carburetor. Then it joins the exhaust manifold on the passenger side.

 

[WebMonkey]

thanks for the quick response.

i had read something like that but couldn't wrap my head how it could figure out how to 'flow' from the driver's side to the passenger side without another valve of some kind up near the engine.



now, i guess i have yet another vacuum line to figure out where it goes!

 

[Turbo4whl]

The side of the cylinder head facing the intake manifold has an exhaust passage that joins the two center exhaust ports through the head.

The vacuum hose should run to a thermal valve on the intake manifold installed in the water jacket, or maybe the thermal valve is in the top of the coolant thermostat cover.

 

[78C10BigTen]

I never knew what that was for when i got my truck but planned headers and duals so i chucked it lol