I had prematurely hit the submit button and posted that "my 239 needs".... after all the insensitive comments and erroneous guesses, I ended up not having anyone supply me with an operating heat riser for my 239 Y Block.


Turns out I have another exhaust manifold that has the heat riser. How is it determined if a heat riser will operate properly?

 

Good question? I hadn't paid much attention to it on the 292 - had it wired open usually, since it didn't seem to "do anything" Will post a link to one test page from Popular Mechanics. The Shop Manual is a little vague too, though similar. It says that the valve should open when "very light finger pressure is applied" and is designed to be open when at normal operating temperature and at high RPM. The counterweight should swing smoothly and easily, but should be in the closed position when engine is cold. Quickly revving the engine should cause it to open briefly.

What I'm not certain, (since it's so cold here right now) is whether the spring will relax enough when engine is at normal operating temperature that the valve will be say, all the way open at idle, or is there still some spring pressure holding the valve partially closed or whatever. It's important that this operates correctly, or better to wire it in the open position, remove entirely. Some claim that the sole purpose is to prevent carburetor icing at a narrow temperature and humidity range - a few extra minutes of warmup takes care of that. The important thing, is make sure it is not rusted or stuck, in the closed position.

https://books.google.com/books?id=D9...ed=0CC4Q6AEwBQ