Headers Comparison - Pipes for Power

If you look at the average power curve numbers, you can see that the larger headers actually made slightly less average power. That's because the horsepower gain at the top did not completely make up for the torque loss at the bottom of the curve. So what's the bottom line here? If this engine is going into a light car with a manual trans and a deep rear gear, or at least an automatic with a stall speed of no less than 3,600 rpm, the larger headers might be a slight advantage. The important point here is that a 131/44-inch header is probably the answer, since it would improve the low-speed power while not sacrificing nearly as much horsepower at the top end.

Another point worth mentioning is that what we're seeing here with these two primary-pipe-diameter power curves is not really as much about power loss or gains as it is about moving the curve around where the engine makes its best power. Had we tested a set of 131/44-inch headers, we're confident we would have witnessed an average power increase over the other two primary pipe diameters. This merely reinforces the idea that engines operate best when outfitted with the right set of parts that complement the rest of the engine package.

Test 7: A 406ci small-block Chevy outfitted with a set of Dart Pro 1 heads, a healthy mechanical-roller camshaft, a set of Hedman 151/48-inch-diameter primary-pipe four-into-one headers, and a 211/42-inch exhaust using a pair of Borla XR-1 mufflers.

Test 8: The same engine outfitted with a set of Hedman 171/48-inch-diameter primary-pipe four-into-one headers with the same Borla exhaust system.