[pokeybritches]

I don't want to leave the NA guys out... stock, 22.5 lb/min (225 hp) mass flow:

2.5" diameter, 3" long = loss of 0.0511 psi, 0.78 hp

3" diameter, 3.5" long = loss of 0.0250 psi, 0.38 hp

3.5" diameter, 4" long = loss of 0.0138 psi, 0.21 hp

I don't think you'll see a 0.57 hp gain on a dyno, or feel it at redline on the street. This is a peak gain, so the average gain will be less.