Do we know if it is actually a bi-metallic spring? The valve on my 56 is kicked open by the exhaust flow as the engine speed increases. I've owned many vehicles over the years and thought they opened by pressure. I don't know????

 

Well that's a good question I guess. The manual describes the heat riser as "thermostatically" controlled, so it would seem to be the case. It should also open at least momentarily while engine is cold, when throttle is winged. That's the pressure part of it. But, be fully open when engine is warmed up - at idle say? That would only happen if the spring was heat controlled as well.

In any case, I need a new one. edit: NumberDummy as usual has answered this before. Ford apparently never sold the spring separately from the exhaust control valve. It looks like other valves use a similar spring and could be made to work.

 

SO .. Question. Now that I have Rams Horn dual exhaust, should the heat riser ports on either side of the intake manifold be blocked off?

I never gave this very much thought. Didn't think it mattered - but tonite I was reading on the H.A.M.B. that doing so makes for a louder exhaust. And this setup is pretty quiet, can't figure out why.