Richard Holdener
July 1, 2009
Our fuel needs were met by a set of 60-pound Siemens injectors. It was necessary to run a spacer plate under the blower to provide room for the taller-than-stock injectors. Note also that we exceeded 1,000 hp with the stock fuel rails!

After installing the 1 7/8-inch headers, the peak power numbers jumped to 735 hp and 636 lb-ft of torque. While all of these values are a great deal to digest, testing the stock GT500 motor did verify that the stock GT500 motor was less responsive to the headers in both NA and supercharged form than the wilder GT1000 combination. Not only that, the NA configurations (both GT500 and GT1000) were more responsive to headers thanks to the presence of the long-runner Cobra R intake (versus the short-runner intake used on the supercharged applications). What all this seems to boil down to is that all applications will benefit from long-tube headers but those equipped with either after market cam timing and/or long-runner intakes will benefit even more.

Supercharged 5.4L Header Test
HP Numbers: 1¾-inch vs 1-7/8-inch vs 2.0-inch (NA 5.4L)
RPM1-3/41-7/82.0
3,{{{600}}}377376377
3,800400400402
4,000427429429
4,{{{200}}}455457458
4,400481483485
4,600506508510
4,800529530533
5,000549550554
5,200568570573
5,400588591593
5,600605608610
5,800617620622
6,000628632634
6,200640643646
6,400651654658
6,600655659663