In fact, typical moderate street performance profiles will readily respond to the tuning effects of headers. Primary pipe length is a consideration, as well. Even at the speed of sound, it takes time for the pressure wave to travel up the pipe. The primary has to be at a length to time the event for the overlap period, but the period of time between cycles varies with rpm. As a result, a given primary-pipe length will tune to a given rpm. The optimal primary-pipe length will vary with the operating rpm range of the engine. Primary lengths between 28 and 42 inches cover the range from high-rpm race engines to tow rigs. Cast-iron exhaust manifolds and shorty headers are at a disadvantage here.

This whole theory has been proven in dyno results on high-output engines, and now we know why. We wanted to explore the question of headers versus manifolds in a much milder setting, a pussycat of an engine if you will-the type of engine that would have a guy questioning whether to use headers or manifolds. To find out, we brought a Mopar Performance 300hp Magnum crate motor to Westech to run some variations. The 300hp crate is a real puppy, with a new-car-like idle (to us) and over 19-inch Hg of vacuum. Its docile nature is the result of a mild cam, with minimal overlap and stock .385/.410-inch intake and exhaust lift, respectively. Spec'd to drop in and go with no hassles, the 360/300 crate will happily pull a full package of accessories, power brakes, air conditioning, and a tightly-converted automatic while idling along effortlessly.

We brought along a wide range of exhaust manifolds and headers, running the gamut from puny stock 318 iron manifolds to the bigger log-type 360 pieces, and even the highly-sought-after and revered 340hp iron units. We also brought a range of headers to see how things would compare. We found some of the results surprising, if not downright shocking. Read on for the results of our exhaustive research.