Vizard states:
"Moreover, both Vizard and Smith teach us that the further one gets from the exhaust port – the cooler the exhaust gases become. As the exhaust gas cools (counter-intuitive to some) it actually decompresses and slows down. Reducing the mid-pipe and tail-pipe size helps to maintain velocity and therefore full system scavenging effects."
That is EXACTLY what I thought of when stepped headers became all the rage.
That's backwards! They need to get smaller, not stepped up to a bigger diameter.
I think it had more to do with header builders saying "Hey, I can build headers faster and easier if I just telescope a bigger pipe over a smaller one rather than going through the hassle of precisely fitting up and butt welding each bend on to the next. I'll market it as STEPPED HEADERS!
In the auto industry we had a saying, "If you can't fix it feature it."
Case in point
