1 ¾-inch Hooker Headers; Long Tube
At this point, things began to get a little weird. Typically, as tube diameter increases, bottom-end power numbers fall while top-end numbers climb. We swapped out the 1 5/8-inch headers for 1 ¾-inch long-tube headers and found additional low-end power from 3,000 through 3,800 rpm, with increases of roughly 4 to 6 lb-ft of torque and horsepower.
In an effort to uncover the abnormal low-end power increase, we measured all header tubes again and used the same No. 5 primary pipe as the comparison. We found the 1¾-inch long-tube headers were approximately ¾-inch longer than those of the 1 5/8-inch units. The longer tubes and the engine's internal timing probably created a low-end power wave that increased the torque and horsepower slightly down low before giving in to the typical power curve.
Either way, this low-end gain was odd and totally unexpected. Once the small-block reached 4,900 rpm, it began moving some serious air and increased the total power again. Had we been testing a high-performance naturally aspirated 7,000-rpm engine, the 1 ¾-inch headers would have revealed their true top-end potential with a broader power gain high in the power curve.
RPM; TQ; Diff.; HP; Diff.
3,000; 422; +7; 241; +4
3,100; 423; +7; 249; +4
3,200; 422; +5; 257; +3
3,300; 422; +6; 265; +3
3,400; 423; +6; 274; +4
3,500; 425; +5; 283; +3
3,600; 425; -2; 295; +3
3,700; 437; +1; 308; +1
3,800; 444; +1; 321; +1
3,900; 448; -2; 333; -1
4,000; 453; -3; 345; -2
4,100; 458; -3; 357; -3
4,200; 462; -4; 369; -4
4,300; 465; -3; 381; -2
4,400; 466; -2; 390; -2
4,500; 467; +1; 400; -0
4,600; 467; +1; 409; -1
4,700; 464; +0; 416; -1
4,800; 462; -1; 422; -1
4,900; 459; +2; 428; +2
5,000; 455; +3; 433; +2
5,100; 450; +2; 437; +2
5,200; 446; +3; 441; +3
5,300; 441; +5; 445; +5
5,400; 434; +5; 446; +5
5,500; 427; +6; 447; +6
5,600; 421; +7; 449; +8
5,700; 411; +5; 446; +6
5,800; 403; +6; 445; +7
5,900; 393; +4; 442; +5
6,000; 385; +5; 440; +4