dyno testing headers

[grumpyvette]

http://www.circletrack.com/enginetech/c ... index.html

http://www.jbaheaders.com/dyno.asp

http://www.revsearch.com/dynamometer/to ... power.html

http://www.highperformancepontiac.com/t ... index.html

viewtopic.php?f=56&t=8401&p=29318&hilit=clogged#p29318

http://www.streetlegaltv.com/forum/kook ... l-904.html

http://www.strokerengine.com/SBCDynoTest.html

http://www.fourwheeler.com/techarticles ... index.html

http://www.moparmusclemagazine.com/tech ... index.html

 

[grumpyvette]

http://www.chevyhiperformance.com/techa ... index.html

1 ½-Inch Flowtech Intermediate-Length Headers

Rather than begin at the bottom and put cast-iron exhaust manifolds on the 383ci for comparison, we figured that anyone with a 440hp stroker wouldn't insult the engine with such restriction. We bolted 1 ½-inch Flowtech headers on the Edelbrock heads. Matching gaskets are part of the Flowtech kit, but we used Fel-Pro pieces because of their reputation for durability and seal efficiency. We were surprised to see that the horsepower was down from the advertised peak number by only 11 hp, and the grunt curve showed in excess of 21 lb-ft of additional peak torque above the advertised number. It appeared that the small-diameter tubing provided some impressive low-end and midrange torque numbers, while the intermediate-length design promoted as much upper-end power as possible to create an outstanding street/strip power curve.

RPM; TQ; HP

3,000; 429; 245
3,100; 434; 256
3,200; 438; 267
3,300; 442; 278
3,400; 445; 288
3,500; 449; 299
3,600; 452; 310
3,700; 455; 321
3,800; 457; 331
3,900; 459; 341
4,000; 460; 350
4,100; 461; 360
4,200; 459; 367
4,300; 459; 376
4,400; 456; 382
4,500; 455; 390
4,600; 454; 398
4,700; 452; 405
4,800; 451; 412
4,900; 447; 417
5,000; 441; 420
5,100; 436; 424
5,200; 430; 426
5,300; 425; 429
5,400; 420; 432
5,500; 414; 434
5,600; 408; 435
5,700; 401; 435
5,800; 391; 432
5,900; 382; 429
6,000; 374; 428

Average; 437; 371


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.
148 0404 Header 03 Z

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

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.

1 5/8 vs. 1 ¾-Inch

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

Average; 438; 375

1 7/8-Inch Long-Tube Hooker Headers With the 1 ¾-inch headers making the Smeding act screwy, we could only imagine what would happen with the big-daddy 1 7/8-inchers. These headers did not come with collector flanges. We put the Hookers to the Edelbrock RPM Performer heads using the favored Fel-Pros and pulled the handle. This time the power numbers danced around like they did with the 1 ¾-inchers and we immediately checked over our previous measurements.

As it turns out, the larger the tube diameter, the more a broad tube bend is required. This in turn lengthens the headers, and in our case resulted in another ¾ inch of total tube length. Again, we felt that this addition combined with the same previous engine-exhaust-wave tuning had something to do with the up and down power curve. If we had ran high-flowing cylinder heads, a huge camshaft, and maybe even a power adder, these big pipes would have shined from 5,500 rpm all the way up.

1 ¾ vs. 1 7/8-Inch

RPM; TQ; Diff.; HP; Diff.

3,000; 430; +8; 246 +5
3,100; 436; +13; 257; +8
3,200; 438; +16; 267; +10
3,300; 436; +14; 274; +9
3,400; 433; +10; 281; +7
3,500; 433; +8; 288; +5
3,600; 435; +5; 298; +3
3,700; 438; +1; 308; +0
3,800; 442; -2; 320; -1
3,900; 446; -2; 331; -2
4,000; 449; -4; 342; -3
4,100; 453; -5; 354; -3
4,200; 456; -6; 365; -4
4,300; 458; -7; 375; -6
4,400; 459; -7; 385; -5
4,500; 459; -8; 393; -7
4,600; 459; -8; 402; -7
4,700; 457; -7; 409; -7
4,800; 455; -7; 416; -6
4,900; 452; -7; 422; -6
5,000; 449; -6; 427; -5
5,100; 445; -5; 432; -5
5,200; 440; -6; 436; -5
5,300; 436; -5; 440; -5
5,400; 432; -2; 445; -1
5,500; 428; +1; 448; +1
5,600; 422; +1; 450; +1
5,700; 415; +4; 451; +5
5,800; 407; +4; 450; +5
5,900; 398; +5; 447; +5
6,000; 390; +5; 445; +5

Average; 438; 374

Conclusion

Our goal was to deliver a straightforward story that would provide readers with a rough idea about what the advantages of real-world header sizing are in terms of power. The odd dyno curves with the larger headers sent us scurrying for answers, and the ones we found pointed us toward internal engine tuning. While this test may have best benefited our Smeding 383ci combination, there is still much to be learned from it.

All of the long-tube designs made more upper-end torque and horsepower than the small-tube pieces, but they also lost power in the midrange relative to where their peak power was made. As for the smallest of the headers tested, we meant to provide a baseline number but instead netted the best overall power curve for a street/strip vehicle. We feel comfortable concluding that the shortest and smallest tube design held true to our initial theories by promoting as much upper-end horsepower as possible with a short tube while building an impressive amount of torque with a small diameter. The four collectors were all pretty much the same, and we didn't test them thoroughly enough to notice any operational differences.

The perfect parts combination is nearly impossible to bolt together the first time. Find an engine combination you like, use the recommendations in this story, and choose a header that's bigger and shorter for the races or smaller and longer for the street. After all, it's not the size of the header that counts--what matters is how you use it.

Parts List

Description; Mfr.; PN

1 ½-inch headers, '73 Camaro; Flowtech; 31108FIT

1 5/8-inch headers, '73 Camaro; Hooker; 2136-1

1 ¾-inch headers, '73 Camaro; Hooker; 2117-1

1 7/8-inch headers, '73 Camaro; Hooker; 2239-1

Stock SBC gaskets, 1.38x1.38-inch; Fel Pro; 1444

Hooker and Stahl adapter plate gaskets for large tube headers, 1.81x1.81-inch; Fel Pro; 1407

Vortec gaskets, 1.50x1.50-inch*; Fel Pro; 1404

LT1 and LT4 gaskets, 1.39x1.41-inch*; Fel Pro; 1470

383ci crate engine;

 

[Indycars]

Much easier to see in graphical form.


Supporting Numbers

 

[grumpyvette]

thank you! once again your proving to be a valued asset on the site as the charts do make it far easier to see the data

ID point out the fact that what many guys don,t understand or realize is that any restriction to exhaust flow AFTER the header collectors significantly reduces the effectiveness of the headers scavenging the cylinders greatly reducing the benefit of having headers installed especially at higher rpms where a restriction in exhaust flow rates can easily cost 50 plus hp or more.
I see guys install killer heads, cams and great intakes but forget to change a restrictive stock exhaust...what goes in needs to go out and that mistake of sticking to a stock exhaust can at times be a huge block to making more hp