# lemans passenger side exhaust manifold flapper valve???????



## bnichols04 (Sep 4, 2007)

i took my passenger side exhaust manifold off (for reasons i wish not to discuss) and noticed that there was some kind of flapper valve that was wire tied closed. what is the point of this valve and is there a way to eliminate this without spending big money going with ram air manifolds or some type of header?


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## gjones (Oct 8, 2012)

*flapper*

That would be the heat riser valve, and is thermostatically controlled (normally a bi-metal spring) and is used for cold weather starts. It'll be closed when cold, directing exhaust gas from the right side through the passageway in the intake, and into the left exhaust bank, heating up the carb for better cold weather drivability. The valve will slowly open as the engine heats up, and be fully open when hot, allowing the right bank to flow freely without going through the intake. If your valve was tied closed, then all right bank exhaust would be diverted through the intake. If anything, they should have tied it OPEN. Depending what kind of carb setup you have,(and what part of the country you live in) you may want to make it fully functional again (if it's not rotted away), or disconnect it altogether (cut the flap out of it, and weld the holes). When I lived up north, I always made SURE that baby was working. (I dare you to try and drive your car at 40 below zero without one!).


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## bnichols04 (Sep 4, 2007)

ok great thanks for the info!


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## kobold (Jan 5, 2019)

Hello guys,
one more question concerning the passenger side exhaust manifold flapper valve:
If there is no (bi-metal) spring (in my case.....), ist the valve normally closed or open ?
The outside-weight (nose) at the valve is (without spring) horizontal.
Did not have problems, just want to know.
regards: Peter


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## kobold (Jan 5, 2019)

Just reply myself.....saw a picture from an exhaust manifold at eBay.
Valve is open without spring.


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## Lemans guy (Oct 14, 2014)

I always revoke those or change manifolds, but have also just wired it open with some mechanics wire on the outside of manifold. It won’t hurt anything. And as long as your exhaust crossover in the intake is not blocked then some heated air from the exhaust will still go into that crossover and provide heat under the carb for better cold weather starting.

lot’s of guys remove the heat riser valve AND block the crossover. Very common on hot rods. Just takes longer to warm up the air fuel mixture.

perfect description by Jones as to how it works. Years ago that often got rusty and rusted shut, what a mess.


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