HRD, most of my "header engineering" has been done on roundtrack racers, and a few 4WD pull trucks. One SuperStock Truck Chrysler 440 we ran turned out 714 HP at 6,500 RPM, after all the humidity and barometric pressure conversion factors were calculated. We figured the volume of the cylinder, and made header pipes to acomodate exactly one cylinderful of exhaust gas for the tuned-length pipes. They were 1 3/4" diameter, equal-length, and 8 feet long, going into a 6" collector. We were going for maximum low-end torque, and we got it in spades! The smallblock Chevy engines we run on the 5/8 -mile banked track at Nashville need short equal-length pipes, into 3" collectors, mated to oval-outlet pipes in front of the rear wheels. We usually come off the banking at 3,500 RPM or so, and wind to 7,500 or more by the end of the straightaway. If the rule-writers allow roller cams anytime soon, we will be able to turn some serious RPM, and the header length will probably change, too!
For street use, headers make about as much sense as a screen door in a submarine. They're not worth the hassle for a little "gee-whiz" appearance impression when the hood is opened. How often does a streetdriven vehicle, especially a truck, run in the RPM range where headers are benefecial?
Jerry
