OK. I have always known that exhaust changes, at least exhaust headers, will improve the performance and power of the motor. That has to translate to better MPG. I think a less restrictive muffler may help MPG also. What keeps me from changing these components is that I DO NOT want any extra 'sound', I hear that as just unwanted noise and droning.

In the past, I have had some success with water injection in carberated motors. That just made a 10% improvement, (big deal 10 MPG to 11 MPG ) in 1975 350 2bbl Ch**y truck. I just think a good water injection system is hard to find for the F150.