u know at first its closed off and running on exhaust gas to warm up the engine. does it open up and allow outside air after it gets to a certain temp or amount of time?

 

What flap are you talking about? There are two the are attached (kind of) to the exhaust. The first being the Early Fuel Evaporative valve down by the Y-pipe, I doubt you mean this one. The other (if you have a carb or TBI engine) is in the snorkel(s) of the air filter housing. It get hot air off the exhaust manifold via a flex tube. Those "flaps" open at a preset temperature set at the factory. Although you can adjust it, I'll see if I can find the tech article someone wrote on the subject (I'm too lazy to go in depth on it right now ).

 

I'm pretty sure he's speaking of the thermac. (That hose thingie running from the exhaust manifold to the snorkel of the air filter housing.)

One thing, though, it doesn't suck exhaust gasses in. The tube leads to a thin metal sheet that's hugging the exhaust manifold, but air can move around it. It just uses the heat of the manifold to warm the air coming in, but it's still outside air it's pulling. At a certain time the valve switches to pull air in from the front of the snorkel. I'm not sure when this happens though, since every Camaro I've had, I replaced the stock assembly for an open element one... heh

 

It is supposed to open at a preset temp. If you follow the vacuum lines from the flapper motor on the air filter to the unit under the air filter housing you will find the unit the controls when the door opens. I have found that they go south. I have blocked vacuum to the sense and the flap is open all the time. It is there to help the carb mix air on cold days. It helps with driveablity. I have found it to cause more troubles because it creates vacuum leaks and no one ever checks this unit. Since my car is put away for the winter I have no problem with cold morning driving.