At normal driving speeds, the exhaust will not add anything. A better flowing exhaust system will only allow the gasses out easer, there will not be anymore or any less then a stock engine can produce.
RPM is controlled by the amount of air and fuel allowed into the cylinders, so unless you are running a lot more rpm, then the amount of exhaust stays the same. Thats why it so important to keep the exhaust pipes small when adding dual pipes. Small pipe holds in heat and heat is what keeps the exhaust gas flowing quickly. Joe
