coppergmc
05-22-2006, 04:50 AM
I found this formula for determining header primary pipe diameter in one of David Vizard\'s books and thought it might be useful.
Take the square root of (CFM X 1.27 / FD).
CFM = flow of the exhaust port at max lift of the cam.
FD = flow density. Use 80 for race engines, 85 for street performance engines, and 90 for regular street engines.
Example: The square root of (190X1.27/80) = 1.73. So a 1 3/4 inch primary pipe header would be best.
Take the square root of (CFM X 1.27 / FD).
CFM = flow of the exhaust port at max lift of the cam.
FD = flow density. Use 80 for race engines, 85 for street performance engines, and 90 for regular street engines.
Example: The square root of (190X1.27/80) = 1.73. So a 1 3/4 inch primary pipe header would be best.