yep. heat riser . supposed to open as the exhaust gets the bi-metal spring hot. useless in my opinion. best thing to do is put it in the full open position and WHAM--WHAM----why you dirty #$%%$%^&* wham--wham-----------------------------tink----------------oh-oh! uh, ya know-ya just can't beat on cast iron like that! maybe best to remove the manifold and take the valve off, and leave the rod so's it don't leak. that's what i do. or, if it's a separate piece, have the exhaust shop remove it next time you need exhaust work, and make a new header pipe. if the stupid valve freezes in the semi-shut position it affects performance in a not so good way. high back pressure is hard on yer valves---and gets you funny looks at the dinner table.
:rolleyes:
