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383 Chevy Small Block Engine - Make 59 LB-FT and 33 More Horsepower For Almost Free!

More power and it's practically for free.

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Test 1 is Hedman 1 3/4-inch headers without the collector extensions. Test 2 is the same headers with the 18-inch collector extensions.

  TEST 1 TEST 2 DIFFERENCE
RPM TQ HP TQ HP TQ HP
2,500 398 189 376 179 -22 10
2,700 395 203 370 190 -25 -13
2,900 392 216 378 209 -14 -7
3,100 384 227 398 235 +15 +8
3,300 381 239 418 263 +37 +24
3,500 385 256 434 289 +49 +33
3,700 392 276 450 317 +58 +31
3,900 401 298 460 341 +59 +43
4,100 429 335 466 363 +37 +28
4,300 455 373 475 388 +20 +15
4,500 477 408 482 413 +5 +5
4,700 488 437 487 435 -1 -2
4,900 491 458 490 457 -1 -1
5,100 489 475 491 477 +2 +2
5,300 484 489 486 491 +2 +2
5,500 476 499 478 501 +2 +2
5,700 465 504 470 510 +5 +6
5,900 452 508 461 518 +9 +10
6,100 441 513 452 525 +11 +12
6,300 433 519 440 528 +7 +9
6,500 425 526 425 526 0 0
6,700 412 526 411 524 - -2
Peak: 489 526 491 528 59 43
Average: 434.9 386.1 446.7 395.8 11.8 9.7
Averages were calculated over the entire power curve with data taken every 100 rpm.

  • 383 Chevy Smalll Block Engine Engine Dyno
    The big gap (arrow) between the Test 1 and Test 2 torque curves is what the header collector is worth in power. You want the triangle curve, not the diamond curve.
    383 Chevy Smalll Block Engine Engine Dyno
    The big gap (arrow) between the Test 1 and Test 2 torque curves is what the header collect
  • 383 Chevy Smalll Block Engine Engine Part
    With our 530hp 383 up on Westech's SuperFlow 902 dyno, we bolted on a set of 1 1/4-inch chassis headers and compared engine performance with and without this 18-inch collector extension. The difference in midrange power was amazing.
    383 Chevy Smalll Block Engine Engine Part
    With our 530hp 383 up on Westech's SuperFlow 902 dyno, we bolted on a set of 1 1/4-inch ch
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