Can someone explain this port please

George Jets said

And yes, remove the heat riser in the passenger exhaust manifold. We take the butterfly and shaft out, then weld the 2 steel sleeves shut to block the holes.

Now the exhaust will free flow out through the exhaust system, and there will be no hot gasses trying to push across the intake manifold ports with the block off gaskets installed.


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I timed my 56 Plymouth with a GTech not long after I got it. 277 poly, four barrel carb, dual exhaust, Powerflite trans and 200 gross horsepower. Ran 18.60. Now I didn't expect it to be fast, but I thought it shouldn't be THAT slow. So, pulled the right side exhaust pipe from the exhaust manifold and, sure enough, the heat riser valve was stuck completely shut. Took it out with some vice grips and a little cussing, left the shaft in. Now it ran 17.80.

Friend said, wow, that's a huge difference. I was kinda surprised it didn't make more difference than that, since with the closed valve, virtually all the right side exhaust (except what little sneaked by the closed valve) was forced into that one little heat riser passage and out the other side into the driver's side manifold. Probably would have made more difference with a more powerful motor.