These are the test results on my@
VitViper Tuned JRSC C38 car. THere are 3 graphs on one plot, so pay attention! Torque is left, hp is right graph.
Dashed blue line: stock exhaust and his previous custom header.
Dotted blue line: stock exhaust and the Ace 4-2-1 header. As you can see, lots of low end gains (particularly below 2500 rpm and from 3200 to 4200 rpm).
Solid green: Perrin 3" exhaust with the Ace header. As expected, the exhaust did basically nothing (not unusual on an S/C car).