Collector Extensions: What Do They Do
For years we have been told of the value of collector extensions when running open headers. No serious drag race car would be running without them. It was simple enough to quantify the benefit of collector extensions while on the dyno, so we ran the 1⅞-inch headers with and without an 18-inch collector extension to have a look. Those old drag racer tales certainly held up, with the extensions producing a tremendous boost in torque. In the 3,000- to 4,000-rpm range, there was more than 50 lb-ft of torque added by the collector extensions. The extensions add to the secondary tuned length of the header, adding heavily to torque at an rpm range that counts. If your plans are to uncork the exhaust at the track, it is definitely worth packing a set of collector extensions.

DYNO RESULTS
Hooker Header Test
427ci Big-Block Chevy
The Torque Numbers
RPM Shorty 1⅞ 2.00 2⅛
3,000 446.4 458.1 466.9 460.2 474.5
3,100 446.5 458.3 468.5 461.8 474.9
3,200 449.7 463.3 472.4 467.5 478.8
3,300 455.2 471.3 478.2 474.6 484.1
3,400 460.8 479.9 484.4 481.2 489.1
3,500 464.2 487.5 489.7 485.8 493.0
3,600 466.9 493.9 494.8 489.8 495.6
3,700 470.3 500.8 499.9 494.8 497.7
3,800 473.7 507.3 503.4 500.7 499.4
3,900 477.2 511.2 504.4 505.6 499.3
4,000 480.9 513.5 504.8 508.3 498.6
4,100 486.2 515.1 506.6 510.2 498.2
4,200 493.1 516.5 510.2 511.8 499.1
4,300 500.8 518.1 514.4 513.3 501.2
4,400 507.9 519.2 518.3 515.3 504.8
4,500 512.8 519.9 522.2 518.3 509.2
4,600 515.6 520.8 526.2 522.3 514.1
4,700 516.9 522.3 530.4 526.0 520.4
4,800 517.8 523.8 534.9 529.3 525.1
4,900 517.8 524.5 537.6 532.2 528.3
5,000 517.1 524.2 538.3 534.7 530.6
5,100 516.2 523.0 537.8 536.3 532.4
5,200 515.1 521.2 536.4 536.9 533.0
5,300 513.2 519.0 534.6 536.1 533.0
5,400 510.4 516.3 532.3 534.0 532.0
5,500 506.1 512.6 529.3 531.4 529.5
5,600 501.2 508.1 525.6 527.9 526.1
5,700 495.6 503.1 521.4 523.6 522.0
5,800 489.6 498.2 516.3 518.3 517.4
5,900 483.8 492.9 511.0 513.0 513.1
6,000 478.4 487.3 505.0 508.8 508.2
6,100 473.0 481.3 498.5 504.0 503.1
6,200 467.3 475.0 492.4 498.8 497.6
6,300 461.9 468.0 485.4 492.8 491.1
6,400 455.0 460.0 477.9 486.3 483.6
6,500 446.7 451.3 469.4 478.6 476.1
6,600 436.9 441.4 459.7 470.2 467.2
6,700 423.7 431.5 449.4 460.1 457.1