Stock Exhaust

This is turning out to be something of a reverse order listing of what I've done but I found the pics from when I originally discovered the stock double wall exhaust configuration. I believe the inside pipe was 1.33" ID so the 1" I've replaced it with should lower the efficient range of exhaust tuning/ engine operating RPM. I believe that if the entire engine's intake and exhaust passage ways could be resized for below 4,000 RPM operation it would yield significant FE gains. Unfortunately this would be quite difficult to do so maybe the next best idea would be to take an engine that was made in different displacements and swap the heads with the smallest ports onto a larger displacement block, this isn't possible with the 1.0 metro engine though. Most engines made today can rev to and produce peak power at 6,000 plus RPMs which means all the ports/ intake/ exhaust passages and cam profiles are sized much too large for low RPM operation, which is where the motor operates for the vast majority of the time. I'm rambling now...