What is this flapper valve blocking my exhaust

[Probesport]

Should the engine be accelerated and the crossover become restrictive, the increased backpressure will blow open the heat riser like the blow-off valve on a turbocharger.

This isn't the best analogy, a turbo bypass or blowoff valve doesn't work that way. Also the heat riser valve itself is thermostatically controlled, once the exhaust warms up the coil, then the valve opens.

You also need to make sure that any aftermarket manifolds you use have a provision for it or the valve is more or less useless.

[Herk]

The riser valve, when functioning is also spring loaded and will blow open under load, minimizing any restriction. The factory choke needs exhaust through the cross-over to release. This is one of those parts like the hot air hose to the air cleaner that costs no power but will cause the engine to run much better and actually saves fuel.

I have experimented with blocking the cross-over and removing the riser valve. No power increase, but cold weather performance suffered greatly.

[tgreese]

... This is one of those parts like the hot air hose to the air cleaner that costs no power but will cause the engine to run much better and actually saves fuel. ...

And vapor recovery. No cost in performance or maintenance, clear benefit.

[FSJunkie]

I expected to see my last post broken up into quotes and ripped apart piece by piece by people who disagree with me and think I'm full of BS by now. This is a pleasant surprise. My arguments against the majority opinion usually don't go this smoothly and it's making me uneasy.

It's like the calm before the storm. It's coming, I know it.

I live in Kansas where it's windy and tornados happen. The wind is always blowing at least a little bit. If it's blowing from the North it will be cold, if it's blowing from the South it will be hot, but it will be blowing one way or another. Sometimes without warning it'll suddenly get absolutely still, and within an hour aa tornado comes down from the heaves and wipes us off the face of the Earth. As a Kansan, that sudden lack of wind sets me on edge because I know its the warning. It's the calm before the storm.

That's what this thread is doing. The wind is still. The tornado is coming. I'm going into my storm shelter now. Y'all have fun.

[serehill]

Not really Junkie

The affects are minimal & as I stated I live in the south where the affects of cold temperature don't effect us as much. The farther you are north the more I see the need.

[FSJunkie]

Ha

At least you understand my humor.

[tgreese]

I expected to see my last post broken up into quotes and ripped apart piece by piece by people who disagree with me and think I'm full of BS by now. This is a pleasant surprise. ...

Oh, no question the function is about warming the intake manifold, and keeping the fuel from condensing. Well stated.