While changing my valve springs I notice when I popped the exhaust valves to seat the locks that I was getting pressure out of both heads from the exhaust crossover. Seems to me that the flow should go on out the exhuast and not reverse back up the opposit header. Am I wrong here? If no more pressure than I had in the cylinder to change the springs was backing up what is it doing when the motor is running? I built my own 2X 2.5 into 3" y pipe and I questioning my design now. I need some input here guys should I go with dual exhaust or order one of Flowmasters high dollar y pipes?