The valve in the exhaust manifold is called a heat riser, and if it wasn't necessary, why would Chevy have manufactured millions of them over several decades? It's there to assist fuel evaporation during engine warmup by directing exhaust gas against the bottom of the intake, then routing those gases downward at normal running temperature to avoid overheating the intake and possibly causing vapor lock or carburetor flooding once the engine is warmed up. If you're willing to tolerate lousy performance during the first 10-15 minutes of operation after every cold start, go ahead and eliminate it.
Jerry

Last edited by Hotrod Lincoln; 07/18/2014 8:46 PM.
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