Aimed primarily at moderate street engines, the 1 3/4-inch Hedman headers were definitely a misapplication on this high-compression, substantially cammed 440. We were interested in seeing how our engine would react to running such a header, and the effects on output. We found the results surprising. At the low end of the pull, the small-tube headers were down considerably in torque, in fact, a staggering 70 lb-ft., from 3,000-3,400 rpm. At 3,400 rpm, they began to recover, and between 4,000-4,500 rpm, they provided the highest torque output of all the headers tested by a slight margin. As expected, above 5,000 rpm, the output dropped rapidly compared to the larger-tube headers. Conventional wisdom predicts that a small-tube header will provide the best low-end torque. In this case, the low-end torque was crippled.
Our test engine has a fairly aggressive solid roller camshaft, on a fairly tight lobe separation angle. That means lots of overlap. The ports had been substantially enlarged, and the induction was comprised of a large plenum single-plane intake manifold, topped with an 1150 Holley Dominator carb. These two factors conspire to make the exhaust system highly communicative with the induction tract, particularly at lower rpm at low induction gas speeds. We suspect that the small header was allowing significant reversion to occur until the dynamic velocity of the induction system reached a critical point, allowing the airflow to "clean-up". Looking at the dyno readout of air consumption, airflow through the engine was down with the decline of output at the low rpm range. Simply put, the header was terribly wrong for this combination at low rpm. We have run this header in tests on engines with outputs more suited to its intended application, in the 400-475hp range and found the results very satisfactory.
|The Pipe||Hedman Hedders' Elite 1 3/4 inch|
|Typical application||Street perfomance|
|Primary diameter||1 3/4 inch|
|Collector diameter||3 inch|
|Primary length||unequal length|
|Peak hp||603 hp @ 6,500 rpm|
|Peak torque||563.9 lb-ft @ 4,800 rpm|
|Average hp 3,000-6,600 rpm||475 hp|
|Average torque 3,000-6,600 rpm||515.2 lb-ft|
|Average torque 3,000-5,000 rpm||508 lb-ft|
|Average torque 5,000-6,600 rpm||526.9 lb-ft|
A proven favorite for Mopar fans, the 1 7/8-inch header typically works very well on a wide range of engine combos, in applications ranging from performance street to fairly serious. With the 1 7/8-inch headers bolted up, the hole at the bottom of the power curve went away. In fact, the 1 7/8-inch tubes had the best output at the bottom of our test range, and held a minor torque advantage over the larger tubes up 5,000 rpm. At about 5,600 rpm, the added flow of the larger tubes made its presence known, but the 1 7/8-inch pipes did carry a significant advantage in this higher range when compared to the 1 3/4-inch tubes. The averages moved up substantially compared to the smaller pipes, indicating the 1 7/8-inch pipes are unquestionably the better choice when dealing in the higher output levels.