Trap Door Inside Exaust Manifold

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weldedrail

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Just wondering what is the purpose of the "trap door" that is inside the passenger side manifold on my 70 dart. It is connected to a round metal wheel on the outside that rotates when the door is opened I assume by exaust forcing it open. What purpose did this serve and how restrictive is it? Am I better off removing it?
 
To help divert warm air to the exhaust crossover in the intake manifold for faster warmup.
 
So what controls this? Is there a linkage or something missing that is supposed to connect to the carb or something?
 
weldedrail said:
So what controls this? Is there a linkage or something missing that is supposed to connect to the carb or something?
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Like green1 said. The spring on the back side of the large round weight is bimetal. That means when it gets hot it expands. As it expands, it causes the valve to open up and divert exhaust more through the exhaust pipe.
 
I'm not sure where Modesto is north or south but if it gets really cold there in the winter you might consider wiring it open to experiment to see if you can live without it on cold start ups. If you need it you can always take the wire holding it open off. If you remove it completely and find you wish you hadn't.......Also if you have a divorced choke that uses manifold heat to warm the spring, it may take longer to warm the spring causing it to be rich longer than it needs to be decreasing your oil change intervals by dumping extra unburnt fuel in the crankcase not to mention decreasing spark plug life.
 
Modesto is in Californias Central Valley. It rarely gets below freezing, supposed to be 92 tomorrow.

I just finnished curing the VHT paint on the manifolds with a heat and cool cycle in the oven. When I pulled it out of the oven at 500 degrees the door was about 75% open. How hot do manifolds get? I would think 500 degrees would be hot enough to open the door compleately.
 
weldedrail said:
Modesto is in Californias Central Valley. It rarely gets below freezing, supposed to be 92 tomorrow.

I just finnished curing the VHT paint on the manifolds with a heat and cool cycle in the oven. When I pulled it out of the oven at 500 degrees the door was about 75% open. How hot do manifolds get? I would think 500 degrees would be hot enough to open the door compleately.
Click to expand...

heat is not an issue in the So cal... lol...
 
weldedrail said:
Modesto is in Californias Central Valley. It rarely gets below freezing, supposed to be 92 tomorrow.

I just finnished curing the VHT paint on the manifolds with a heat and cool cycle in the oven. When I pulled it out of the oven at 500 degrees the door was about 75% open. How hot do manifolds get? I would think 500 degrees would be hot enough to open the door compleately.
Click to expand...

The exhaust pressure is what opens the valve. At idle it's almost completely closed and opens progressively more as your exhaust flow increases. At idle it's almost closed causing the hot gases to remain partially trapped in the exhaust crossover in the intake manifold thereby warming the area under the choke spring more quickly. If you totally remove the valve, the choke spring will not heat up as fast and it will keep the choke on longer than necessary thereby keeping a rich mixture longer than you need. All that unburnt fuel has to go somewhere some out the tailpipe and the rest in the motor.I live in Fl so I haven't ever run a choke on a performance application. It doesn't sound like where you are it gets too cold. I don't think in your situation you are losing that much horsepower by leaving it alone. Although I have never seen dyno results to prove it, I have been told that the extra hot gases going through the intake will cause the intake manifold to be hotter thereby decreasing the density of the fuel charge and reducing the performance. That is why many intake manifold gasket kits have a small steel shim that you can place over the crossover ports to stop the hot gases from passing through.Or you could do as I said before wire it open and try it, if its too rough or rich "unwire it".
 
You definitely want the manifold heat system working. It's a common but mistaken notion that blocking it off or removing it on a non-race vehicle is beneficial. You could get around its necessity to operate the automatic choke (no, the intake will not get hot enough to open it on its own without exhaust heat) by installing the applicable electric choke kit (link is for slant-6s; they have them for V8s, too) but you still want it operational even if you have a manual choke or none at all. See this post and this one.
 
dustoff440 said:
The exhaust pressure is what opens the valve.
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Sorta. When the engine is cold in cold weather, trust me, unless you STAND on it, that bimetal spring will limit the amount the valve opens. That's its purpose. Besides, you're not supposed to be abusin a cold engine anyway. It's not good for it.
 
I operate a lil differently.... I installed an electric choke and I have headers so there is no back pressure to keep the heat AND if it isn't at least 65 and sunny, my classics don't leave the garage. Also, being raised in Detroit and around cars my entire life, it is kind of a given that you do not "get on it" when everything is COLD.....thats just being DUMB!
As far as the heat risers are concerned I make a point of removing them and pluggin the holes, they are nothing more than a chronic hassle, they malfunction they get stuck closed and they are NOT reliable in the least. I typically dont disagree with Dan, he is quite knowledgeable but in this case once the motor is up to operating temp, it is well past the temp to vaporize gasoline, hence the hassle and problems associated with the riser out weigh the efficiencies realized with the riser. I know quite a few registered master mechanics in the Detroit area and not one of them appreciates the minor benefits of the heat riser, in fact they are widely despised here in Michigan. It is rare to see one intact on most classics in and around Detroit. I will not disagree that there are benefits, especially if you drive in cooler to cold weather. BUT the benefits are seriously out weighed by the hassle and most folks round here don't use their classics as "dailys" esp in the winter months. I guess the point is removing them is not a critical threat MHO
 
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This is sometimes called the Heat Riser Assembly.

On old cars & trucks it sometimes rusts up and stays frozen.

There often is a Counterweight that aids in the function.
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Well, the manifolds are on the car now and I can play around with it in the future, might wire it open and see if that makes any difference. This dart was my daily driver for many years but in its restored condition I can't see it doing much daily driving in the winter.
 
My line of thinkin says if it works, why mess with it? But that's just me.
 
Mine was froze shut, it was removed by me, after I removed the dead 273
and installed the rebuilt 318, into my 1964 Valiant.

One less thing to act up, this was the second one I found frozen shut. :(

ce44.jpg
 
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