It might be possible to route exhaust gas from one section of the header to the other, using the alternating pressure pulses from each exhaust pipe. The stock heat riser arrangement uses a flapper valve in the exhaust stream to direct the hot gases either toward or away from the bottom of the intake depending on the position of the weight and spring. With the headers and the piped heat, it would not be possible to stop the flow of gas under the intake once the engine warms up, resulting in too much heat to the incoming mixture. The only time manifold heat is needed is for a few minutes during warm-up, so unless some type of cutoff valve is incorporated into your piping system, the intake will get heated all the time, not when it's actually needed. That's just one of many reasons headers don't belong on a street machine.
Jerry
Edit: My comment about not getting exhaust gas in a heater tube was a result of misreading the original question. Some automatic chokes use heated air from around the exhaust manifold to help release the choke. People have drilled into the exhaust stream for this purpose, which does severe carburetor damage almost instantly. Sorry about the misunderstanding!
Jerry
Last edited by Hotrod Lincoln; 01/25/2009 4:58 AM.
