Manifold heat control valve.

No expert but that looks right to me based on our current project......when the spring heats up the flapper should direct the exhaust flowdown and out.....cold, its "vertical", directing exhaust up into the hot box.

did you replace your spring or refurbish what you have? Ours broke and couldnt find the replacment kit anywhere for less than a couple hundred bucks so I just bought a Dorman manifold .