At about how many rpms is this thing supposed to start opening? i wish i had a picture of the valve in a manifold, but i couldn't find one, so i will ask this here: does the valve/flapper restrict the exhaust flow ? i assume there's a passage where exhaust flows around the valve plate but how big is it? is the type with the square counterweight more desirable? this is on a 1983 engine with super six package. also i would imagine this valve makes the exhaust quieter.

correct me if I am wrong here guys, but I thought the heat riser was thermally operated, and not related to engine rpm.

Correct?

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-76 Cordoba, 360 4bbl
-68 Valiant, 273 2bbl
-67 Dart /6 4bbl, Leaning Tower of Power!!!

The '71-up round-counterweight heat riser system was designed to remain in "heat on" position up to a vehicle speed of approximately 30 mph with the engine at normal operating temperature. This is for driveability, mileage, and emissions reasons (hotter intake manifold = more thorough vapourisation of fuel).

Both the early and late heat risers remain in "heat on" position up to about 40 mph or so when the engine's cold.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Interesting. Who'd a thunk it?

Thanks Dan

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-76 Cordoba, 360 4bbl
-68 Valiant, 273 2bbl
-67 Dart /6 4bbl, Leaning Tower of Power!!!

here's another question.....I have a 74 dart with a holley 1945 carb......heat riser spring broken and heat riser just stays in open position I assume.....car runs horribly when first started (sputters) but runs great after warm up......how much better would it run cold if I did something about heat riser....seems I recall there may be no way to fix it other than replacing exhaust manifold.......thanks for comments....also is 1945 carb part of problem.......vic

Your poor cold running is probably a combination of no manifold heat and problem(s) with the choke system. See choke article. An Electric choke kit would bring adjustability to the choke system (the present setup is not adjustable). Also check that your thermostatic air cleaner system is intact and working correctly, supplying warm air to the carb until the engine has fully warmed up.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

dan, thanks for the info......I've had the choke article in my files a long time and have adjusted the choke accordingly.....mostly in terms of the "u" in the operating link..........I've put off dealing with the heat riser for about 2 years now because it involves replacing the exhaust manifold and what is involved and the fact that I always allow about five minutes of warm up before I drive the car for the first time.....the first car I ever bought was a 64 dart with a 170 slant and it didn't run well when first started in the winter even though it was new......oh well........vic