To get a handle on the variations in power output with a typical high-output street engine, we gathered a wide range of popular big-block Chevy headers from Hooker. Represented were 1¾-, 1⅞-, 2.00-, and 2⅛-inch full length headers, all with Hooker's factory silver ceramic metallic coating. To judge the effect of the header coating, we also had on hand a set of plain black painted 1⅞-inch headers identical to the coated version for a back-to-back test. We completed the lineup with a set of Hooker Block Hugger shorty headers, also in a 1⅞-inch primary tube diameter. Our test engine is a high-performance street big-block Chevy based upon a stock stroke 427. The engine was built with just under 10:1 compression, a pair of AFR 305 "as-cast" cylinder heads, a Crane 246/254 duration-at-.050-inch Street Roller cam, an Edelbrock Victor single-plane intake, and a Holley 950-cfm Ultra HP 4150 carb. Here is how the various pipes stacked up.

As the numbers show, there was quite a lot of power to separate the various header configurations, with as much as a 39hp spread in peak-to-peak horsepower, between the shorty header and the best performing long-tube, the 2.00-inch. The shorty header certainly did not provide the same exhaust tuning and scavenging effect of any of the long-tube headers, with a significant loss in torque and power throughout the curve. Our smallest full-length header, the 1¾-primary pipes produced substantially more power throughout the rpm range, and a particular advantage in torque in the 3,500-4,000 rpm range. For all-out power, the long-tubes win, but in many installations the shorty headers are a much easier fit.

Getting into the various full-length headers, bolting on the 1⅞-inch headers brought into focus the shortcomings of the smaller headers. The larger pipes showed a healthy increase in top end power of 21 peak horsepower, while even managing a torque advantage right from the bottom of our test range of 3,000 rpm. The smaller pipes had a short-lived advantage in the 4,000-rpm range, but the average power gives the nod to the larger pipes. Stepping up another level to the 2-inch headers showed another gain in top end power, this time a more modest increase of 11 hp at the top of the power curve. At the lower rpm levels, these two headers swapped the torque advantage depending upon the engine speed. Moving to our largest header, the 2⅛-inch primary, we seemed to be reaching the point of diminishing returns. As with our previous test, these headers swapped for torque advantage through the lower rpm range, while at the top end the larger tubes were actually slightly down on peak power. Overall, the big pipes were an overkill, sacrificing fit and packaging for no real gain.

Coatings: Are They Worth It?
As a part of our test, we wanted to quantify the benefits of a coated header versus a plain uncoated black painted header. A thermal barrier ceramic coating adds considerably to the price of any header, often doubling the price. We tested two otherwise identical Hooker 1⅞-inch headers with surprising results. Running on the dyno, we found the power numbers virtually unchanged (see Average Power table on next page). Where the ceramic coating made a remarkable difference is in the heat transferred by the header. We tested the header temperature immediately after a run, and then one minute after shutdown. The coated headers measured 258 degrees F dropping to 195 degrees F a minute after shutdown. In contrast, the uncoated header measured a scalding 870 degrees, retaining 520 degrees a minute after shutdown. We didn't need a heat gun to tell the difference in the test cell.

Our next test loaded the engine to 60 lb-ft of torque at 2,800 rpm, simulating a high-speed cruise situation. We gauged the surface temp of the header once fully stabilized. Once again, the difference was huge, with the coated header showing 288 degrees, while the uncoated header recorded 850 degrees. While the dyno run didn't show much difference in output, an engine breathing air from under the hood will definitely feel the effects of that extra 562 degrees F pumping into the engine bay. Taking account the effects of heat on engine component life and passenger comfort, the coated headers are definitely a winner.