exhaust manifold heat valve

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#16

05-28-2014, 06:45 AM

redroad

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here is a picture of the manifold .. Better flowing than the light duty and a worthy consideration for a stationary motor .. Notice the three bolt pattern on the bottom flange .. You can still buy these new

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#17

05-28-2014, 08:05 AM

redroad

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From the 1976 Ford truck shop manual Vol.2 engine 29-01-2 and 29-01-03

 Exhaust Heat Control Valve (Spring Operated)
If fuel condenses on the cold surfaces of the induction system, air-fuel ratios fluctuate. These variations can cause uneven acceleration and increased emission levels. The exhaust control valve used on some engines is designed to provide quick induction system warm-up and better cold engine air-fuel ratio control. The thermostatically controlled valve is located between the exhaust manifold and one branch of the exhaust pipe.
While the engine is cold, the valve is closed and routes hot exhaust gas through a passage under the carburetor. This quickly warms the air-fuel mixture delivery passages, thus providing improved air-fuel ratio control. As the engine warms up and the valve opens, this action reduces exhaust gas flow through the warm-up passage to prevent excessive heat.
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#18

05-28-2014, 10:34 PM

raven3

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On the HD exhaust manifold , appears to incorporate a passage way to the intake manifold without a coil spring loaded flapper valve.

So why does the light duty manifold incorporate the flapper and the HD does not?

Maybe the light duty is designed for short runs with minimal warm up time while the HD is designed for long haul with additional initial start up wait time to stablize temperature of intake manifold before placing engine under load.

The explanation on the 76 indicates "flow". There is no air flow because the two cavities in the intake manifold are closed ended with no exit passage to develop air flow.
However, there is heat conduction flow.

Would argue that with the flapper in the horizontal position( engine cold), allows heat conduction flow to both inner and outer intake manifold cavities with gaps between the flapper plate and the exhaust manifold. With flapper in the vertical position,( engine hot) conduction heat flow is eliminated to the outer intake manifold cavity, while heat conduction flow is allowed to the inner intake manifold cavity with gaps between the flapper and the exhaust manfold. The flapper covers the passage way to the outer intake manifold cavity with no gaps between the flapper plate and the exhaust manifold.

There is more heat transfered to the intake manifold with the engine cold than when the engine is hot.

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#19

07-24-2014, 03:24 AM

hermancm

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Up here in northern WI we went below zero 63 times last winter... Brr! I need a replacement manifold heat valve too. I see Rock Auto has them but that vacuum actuator might be something to get, any idea where a cold northerner might find one?

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