It is my understanding that any engine with too short an exhaust will allow cool air to be drawn back up into the tube which warps the exhaust valves and depending upon overlap amount even an intake valve with the uneven cooling. I seem to remember somewhere a minimum length of some 24 inches from the head as recommended for best life. Also the pipes sharing the same area/joining together makes the xhaust pulses help each other accelerate out of the pipe provided it is sized correctly, which will increase power especially in mid to high rpm ranges. This is the reason Flowmaster mufflers and others work. They create suction using the pulses to draw more pulses and so on....
Colin & Bev Rainey KR2(td) N96TA Sanford, FL [email protected] http://kr-builder.org/Colin/index.html
