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Originally Posted by priobe
Jac mac,
Are you referring to match porting?
My heads have been ported and polished and port matched to the headers.
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Yes & NO.
Match porting is when the builder ensures the exhaust header port is the same size as the port of the cylinder head.
In creating an ANTI REVERSION set up we intentionly create a mis match as per dwg's 'C' or the cones in dwg's 'A&B'. In this way it is easy for the exhaust gas to exit the port but difficult for the reversion pulse gas, which tend's to travel back toward the engine along the short side radius or low activity areas of the pipe where it contaminates the incoming fuel mix during the overlap period .With Anti Reversion we reduce the amount of this contamination and get a smoother running engine at lower RPM.
Jac Mac