Any exhaust system is a compromise, whether it's a factory cast iron manifold, or some sort of header. Based on the results my family's race team has documented on the dyno since the early 1950's, headers can make a considerable difference in horsepower and torque- - - -either adding or subtracting it. Gas flow from the air cleaner to the end of the exhaust system must be considered as a whole, not just the performance of the header. Generally, the longer the individual exhaust runner is, the better the low-end torque will be. Shorty header pipes build lots of top-end horsepower, and severely restrict low end torque. If your street machine is going to spend most of its time wound up tight in 1st. or 2nd. gear, go for the headers.
The best-performing headers I ever used were custom made for a 440 Dodge engine in a pull truck. All 8 tubes were equal length, and just a shade over 8 feet long each. They helped us develop a massive amount of torque to break away and get the sled moving. The engine topped out on the dyno at 714 horsepower at 6500 RPM, corrected for temperature and humidity, on one Quadrajet carburetor and gasoline. We won a bunch of truck pulls with that engine!
Jerry
