Trap Door Inside Exaust Manifold

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.

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".