What is this?

[y5mgisi]

As im typing this, im sure somone else is also...

Its a heat riser valve. Vacuum is applied to the diaphragm(the big can thing with the nipple on it) and closes a butterfly valve. This forces all the exhaust gas threw the head, intake, and out the other head warming the engine up faster in cold weather. The vaccum line should be in line with a thermostatic vacuum switch that will shut vacuum off once the truck warms up and therefore, re open the butterfly valve. Between the exhaust manifold and exhaust pipe is a piece smiler to this,


thats what the diaphragm is opening via a rod that goes from the diaphragm to the butterfly valve.