1 5/8-Inch Hooker Long-Tube Headers
After such great results from the intermediate-length headers, we were curious to discover what the 1 5/8-inch long-tubes would provide. Typically, a 1 5/8-inch long-tube header is the ideal choice for street/strip engines making upward of 450 hp, but with the previous numbers looking so good, we admit that the Flowtech stuff had us guessing.
But now we changed the testing parameters, sporting a 34 ¼-inch No. 5 primary as compared to the 17-inch No. 5 primary of the 1 ½-inch collector. After a few pulls, the 1 5/8-inch headers showed that the average power numbers gained 1 lb-ft of torque and 1 hp, and did so by giving up a significant amount of power on the bottom end.
From 4,100 rpm on up, the engine pulled hard, posting two new peak power readings of 468 lb-ft of torque and 441 hp. Though the total power gains carried on longer than the losses, the average power increase is insignificant when compared to the amount of lost low-end power a street/strip car could use. With a drop of as much as 29 lb-ft of torque between 3,000 rpm and 4,000 rpm, the 383's in-car acceleration characteristics would suffer dramatically and hardly make up for it on the top end.
It's clear that this particular engine is happy with shorter, smaller primaries than with longer, larger tubes. The less-than-ideal street/strip performance could be attributed to cam timing, intake-runner design, piston size, piston speed, and many other engine-related tuning factors. Rather than changing the parts combinations to pump up the bottom-end power numbers, we further increased the header size on our Smeding 383.
1 ½- vs. 1 5/8-Inch
RPM; TQ; Diff.; HP; Diff.
3,000; 415; -14; 237; -8
3,100; 416; -18; 245; -11
3,200; 417; -20; 254; -13
3,300; 416; -26; 262; -16
3,400; 417; -28; 270; -18
3,500; 420; -29; 280; -19
3,600; 427; -25; 292; -18
3,700; 436; -19; 307; -14
3,800; 443; -14; 320; -11
3,900; 450; -9 ; 334; -7
4,000; 456; -4; 347; -3
4,100; 461; +0; 360; +0
4,200; 466; +7; 373; +6
4,300; 468; +9; 383; +7
4,400; 468; +12; 392; +10
4,500; 466; +11; 400; +10
4,600; 466; +12; 408; +12
4,700; 464; +12; 415; +10
4,800; 461; +10; 421; +9
4,900; 457; +10; 426; +9
5,000; 452; +11; 431; +11
5,100; 448; +12; 435; +12
5,200; 443; +13; 438; +12
5,300; 436; +11; 440; +11
5,400; 429; +9; 441; +10
5,500; 421; +7; 441; +8
5,600; 414; +6; 441; +6
5,700; 406; +5; 440; +5
5,800; 397; +6; 438; +6
5,900; 389; +7; 437; +8
6,000; 380; +5; 434; +6
Average; 436; 372