Originally Posted by Brabs_Weather
This decrease in velocity will slow the gasses from exiting the exhaust , which should cause pressure to increase slightly.
This is also true, which is good for torque. Notice the difference between Red and Focusboys dyno charts. While there are many contributing factors, the header makes a huge difference in the torque curve. Or, in Focusboy's case the lack thereof. His table-top torque curve should represent an increased driveability.