Years ago I dyno tested a 426 M.W. pump gas street motor on a new DTS engine dyno, the shop did not have a set of dyno headers made up yet so we used a set of Hooker A body 1 7/8 primary tubes about 40 inches to the collectors and 3.5 inch colletors for the first 23 pulls while the shop made up a set of dyno headers. The shop made a set of 2 1/4 primary pipes that where around 25 inches long and 4 inch collectors for there dyno headers, we swap the headers with no other changes and the motor pick up HP all the way thru the RPM range, 3500 to 6500 and lost some torque down low, below 4000 rpm, on the averages the bigger headers made more torqure and HP than the smaller tube set made