We could fill volumes spelling out the number of factors that affect an internal combustion engine's performance. Each component, each setting, each measurement and tolerance of every type combine to create a powerplant's performance characteristics. As we've said many times before, however, nothing defines the character of an engine more than its camshaft. Of all the measurements and specifications found in a camshaft, it's hard to underestimate the importance of the lobe separation angle, or LSA. Simply put, the LSA indicates the angle, in camshaft degrees, between the maximum lift points, or centerlines, on the intake lobe and the exhaust lobe. This figure, which is ground into the cam at the factory and cannot be changed, directly influences an engine's powerband. It's more complicated than that, of course, but the idea behind this project is straightforward. In short, we hit the dyno with our Coast High Performance 406 stroker test mule and tested three camshafts that carried identical specification-except for their lobe separation angles. How did it affect our engine's powerband? Read on to find out.

As we worked with Comp Cams engineer Billy Godbold to spec out this experiment and interpret the results, we were looking to discuss this complicated subject as simply as possible. For Godbold, this started with the term lobe separation angle. "It's doesn't mean anything except for how it affects the camshaft centerlines," he explained. "You determine the centerlines, which determines overlap, and that has performance effects." To be more specific, every cam lobe has a given number of degrees of duration, and there is a midpoint to this event. This midpoint is referred to as a centerline, and there is one for the intake and one for the exhaust. The intake centerline is used to position the cam in the engine. The exhaust lobe centerline doesn't come into play during installation or cam degreeing, but it is essential to calculating lobe separation angle. The LSA is calculated by adding the intake centerline and the exhaust centerline, then dividing by two. For example, a cam with a 106-degree intake centerline and a 114-degree exhaust centerline has a lobe separation angle of 110 degrees (106 + 114 = 220; 220 2 = 110). In fact, the cam we already had in this 406 was a standard Comp XR300HR with a 110-degree lobe separation. Our other two 'sticks were custom ground to have all the same specs as our 110-degree specimen, except that one had a 107-degree LSA and the other a 113-degree LSA.

Quick Notes
What We Did

Dyno-tested three camshafts with identical specs except for lobe separation angle.

Bottom Line
The effects are subtle, but lobe separation angle does affect an engine's powerband.

Price
Only the power you give up by choosing the wrong LSA.

Or rather, almost all the same specs. The reason that changing the LSA changes overlap is because it also changes the four valve timing points found on a cam: intake opening (IO), intake closing (IC), exhaust opening (EO) and exhaust closing (EC). "The timing points are what the engine responds to," said Godbold. Intake closing is considered the most important point of the four, since it does the most to establish where peak torque occurs. An early IC improves low-speed torque, but limits high-rpm power since it also limits time for cylinder filling. On the other hand, a later IC allows more time for a cylinder to fill at high rpm, but limits low-end torque since cylinder pressure is pushed back through the intake port. Intake opening (IO) plays a big part in establishing overlap (the time when both intake and exhaust valves are open). An early IO increases overlap and can lead to a sluggish engine, since the intake charge is contaminated with exhaust gasses. A later IO reduces overlap, improves idle quality, and increases low-speed torque. Exhaust opening (EO) ranks second only to intake closing in affecting engine performance. An early EO can limit low- and midrange power by allowing torque-creating cylinder pressure to escape, but helps high-rpm performance by creating more time for exhaust gas to be expelled. Exhaust closing (EC) also affects overlap. An early EC reduces overlap, improving idle but limiting midrange power. A late EC increases overlap, which hurts idle but helps high-rpm power. All of these figures can be found on a cam card, and we've listed them here for you to puzzle over as you compare dyno runs. In short, this all brings us back to overlap. "You change the timing points with lobe separation," reiterates Godbold. So with that in mind, we present the simple version of what changing an engine's LSA does (see "Lobe Separation Angle Effects" sidebar).

So how did all this theory play out in our test scenario? Our methodology was straightforward: We ran each cam in our 406, making pulls with both Dart single-plane and dual-plane intakes mounted up. According to Godbold, the LSA changes did "exactly" what they should do in our application. "When you spread the LSA, you move out the two most important points (intake closing and exhaust opening). This makes the cam act bigger when it is ground on a wider lobe separation. Likewise, a narrower lobe separation moves the IC and EO points closer together, making the cam act slightly smaller. Hence, the 107 LSA cam was better at low rpm and the 113 LSA cam was worse at low rpm. This motor liked the overlap."

Our dyno figures bear this out. The 406 made more low-end torque with the 107 LSA cam, regardless of the intake manifold it was wearing, and held its own at higher rpm. In the same vein, the dual-plane equipped 406 had better results with the 107 LSA cam. "The dual-plane reacted to lobe separation almost exactly as it would to a smaller camshaft," said Godbold.

The 113 LSA cam, on the other hand, made less power everywhere and especially fell on its face with the single-plane intake. "I'm not totally sure if the reason is simply a result of the shorter runner length with a single-plane, or if you could trace it back to the common plenum," Godbold observed. "However, I do know for certain that single-plane manifolds have always run best with tighter lobe separation camshafts."

The 113 LSA cam may have made more power at high-rpm, but we ran into valve bounce issues with our hydraulic roller motor at 6,600 rpm, so we weren't able to find out. In most cases, though, the power given up on the lower end wouldn't have been worth the bit we gained near 7,000 rpm. The 110 LSA cam made the most peak power-609 hp with the single-plane. Its numbers were much closer to the 107 LSA cam's figures, but the narrower LSA still put out more horsepower and torque below 6,000 rpm. It's probably not a coincidence that Comp utilizes a 107-degree LSA in its Thumpr line of cams.

Godbold thinks it would be revealing to do the same test with a much smaller set of three cams in the same application. "Then I think you would see a wider power range on the wider separation cam," he observed. "I still think 107 would give you the best peak numbers, but the wider separation cams tend to fall off less beyond peak power." With smaller cams running at a lower rpm, we'd probably be able to see that. But for now, we've got a very clear demonstration of the advantages-namely a more usable powerband-of running a narrower LSA.

LOBE SEPARATION ANGLE EFFECTS
NARROWER LSA WIDER LSA
Increased overlap Reduced overlap
Increased low-rpm torque Improved top-end power
Narrower powerband Wider powerband
Reduced idle quality Improved idle quality
Increased cranking compression Reduced cranking compression
Decreased piston-to-valve clearance Increased piston-to-valve clearance
406 STROKER SPECS
Displacement 406.0 ci
Bore x stroke 4.155 x 3.750
Rotating assembly Probe forged steel crank
  and rods
Pistons Probe forged
Heads Dart Pro 1 227 CNC
Compression 11.1:1
CAMSHAFT 1
107º LSA Comp Cams Hydraulic Roller
PN 12-000-8
Grind No. CS 3318S/3319S HR107+4
Gross valve lift 0.562/0.580 intake/exhaust
Valve lift w/ 1.6 rockers 0.600/0.619 intake/exhaust
Duration at 0.050 248/254 intake/exhaust
Valve timing (@ 0.050 lift) Open Close
Intake 21 BTDC 47º ABDC
Exhaust 58 BBDC 16º ATDC
Vacuum at 1,000 rpm 6 in
CAMSHAFT 2
110º LSA Comp Cams Hydraulic Roller
PN 12-444-8
Grind No. XR300HR
Gross valve lift 0.562/0.580 intake/exhaust
Valve lift w/ 1.6 rockers 0.600/0.619 intake/exhaust
Duration at 0.050 248/254 intake/exhaust
Valve timing (@ 0.050 lift) Open Close
Intake 18 BTDC 50º ABDC
Exhaust 61 BBDC 13º ATDC
Vacuum at 1,000 rpm 7 in
CAMSHAFT 3
113º LSA Comp Cams Hydraulic Roller
PN 12-000-8
Grind No. CS 3318S/3319 HR113+4
Gross valve lift 0.562/0.580 intake/exhaust
Valve lift w/ 1.6 rockers 0.600/0.619 intake/exhaust
Duration at 0.050 248/254 intake/exhaust
Valve timing (@ 0.050 lift) Open Close
Intake 15 BTDC 53º ABDC
Exhaust 64 BBDC 10º ATDC
Vacuum at 1,000 rpm 8 in
The numbers: Dual Plane vs. Single plane
DYNO DETAILS
Carburetor Holley 950 Ultra HP 75/79 jets with 1-in open spacer
Ignition MSD 7AL Digital
Headers Hedman 1 3/4-in long-tubes with 18-in extensions
Fuel 91-octane unleaded
Timing 37
Intake manifold Dart dual-plane
DUAL PLANE
107º LSA 110º LSA 113º LSA
Avg. torque 492 lb-ft Avg. torque 485 lb-ft Avg. torque 480 lb-ft
Avg. power 449 hp Avg. power 442 hp Avg. power 439 hp
RPM LB-FT HP RPM LB-FT HP RPM LB-FT HP
2,500 417 198 2,500 409 194 2,500 397 189
2,600 419 207 2,600 411 203 2,600 398 197
2,700 429 220 2,700 420 216 2,700 408 210
2,800 444 237 2,800 433 231 2,800 421 225
2,900 458 253 2,900 448 247 2,900 435 240
3,000 467 267 3,000 459 262 3,000 446 255
3,100 477 282 3,100 470 277 3,100 455 269
3,200 482 294 3,200 477 291 3,200 464 283
3,300 485 305 3,300 481 302 3,300 471 296
3,400 488 316 3,400 485 314 3,400 475 308
3,500 494 329 3,500 489 326 3,500 479 319
3,600 501 343 3,600 495 339 3,600 485 333
3,700 510 360 3,700 502 353 3,700 492 346
3,800 518 375 3,800 509 368 3,800 498 361
3,900 524 389 3,900 514 381 3,900 504 374
4,000 529 403 4,000 520 396 4,000 508 387
4,100 534 417 4,100 525 410 4,100 513 400
4,200 537 429 4,200 529 423 4,200 518 414
4,300 539 441 4,300 532 435 4,300 521 427
4,400 539 452 4,400 532 446 4,400 523 438
4,500 538 461 4,500 532 456 4,500 523 448
4,600 540 473 4,600 533 467 4,600 525 460
4,700 540 483 4,700 533 477 4,700 525 470
4,800 540 493 4,800 533 487 4,800 526 481
4,900 539 503 4,900 533 497 4,900 526 491
5,000 538 512 5,000 531 506 5,000 526 500
5,100 536 521 5,100 530 515 5,100 524 509
5,200 534 529 5,200 529 523 5,200 522 517
5,300 532 536 5,300 526 531 5,300 520 525
5,400 529 544 5,400 524 539 5,400 518 532
5,500 524 549 5,500 520 544 5,500 515 539
5,600 519 554 5,600 516 550 5,600 512 546
5,700 514 558 5,700 511 554 5,700 507 550
5,800 510 563 5,800 505 558 5,800 502 554
5,900 503 565 5,900 499 561 5,900 496 557
6,000 496 566 6,000 494 564 6,000 492 562
6,100 488 566 6,100 485 564 6,100 485 563
6,200 480 567 6,200 479 566 6,200 477 564
6,300 473 568 6,300 472 566 6,300 470 564
6,400 466 568 6,400 463 565 6,400 463 564
6,500 458 567 6,500 455 563 6,500 456 564
6,600 450 566 6,600 448 562 6,600 447 562
6,700 441 563 6,700 435 555 6,700 439 560
6,800 433 561 6,800 417 540 6,800 430 557
6,900 421 553 6,900 400 526 6,900 419 550
7,000 408 544 7,000 389 518 7,000 400 533
7,100 397 537 7,100 379 513 7,100 386 522
SINGLE PLANE
107º LSA 110º LSA 113º LSA
Avg. torque   495 lb-ft Avg. torque   491 lb-ft Avg. torque   481 lb-ft
Avg. power   456 hp Avg. power   452 hp Avg. power   445 hp
RPM LB-FT HP RPM LB-FT HP RPM LB-FT HP
2,500 419 199 2,500 417 198 2,500 386 184
2,600 420 208 2,600 417 206 2,600 392 194
2,700 424 218 2,700 421 216 2,700 399 205
2,800 431 230 2,800 426 227 2,800 404 215
2,900 439 243 2,900 430 238 2,900 407 224
3,000 449 256 3,000 439 250 3,000 417 238
3,100 456 269 3,100 451 266 3,100 428 253
3,200 461 281 3,200 459 280 3,200 438 267
3,300 465 292 3,300 464 292 3,300 452 284
3,400 468 303 3,400 467 302 3,400 456 295
3,500 471 314 3,500 468 312 3,500 460 307
3,600 478 327 3,600 474 325 3,600 465 319
3,700 485 342 3,700 483 340 3,700 471 332
3,800 491 355 3,800 487 352 3,800 473 342
3,900 495 367 3,900 488 362 3,900 473 351
4,000 498 380 4,000 492 375 4,000 479 365
4,100 506 395 4,100 499 389 4,100 484 378
4,200 514 411 4,200 507 405 4,200 491 393
4,300 520 426 4,300 516 423 4,300 499 409
4,400 526 441 4,400 521 437 4,400 505 423
4,500 528 452 4,500 524 449 4,500 512 438
4,600 533 467 4,600 527 462 4,600 519 455
4,700 535 479 4,700 531 475 4,700 523 468
4,800 539 492 4,800 534 488 4,800 526 481
4,900 541 505 4,900 536 500 4,900 529 494
5,000 543 517 5,000 538 512 5,000 529 504
5,100 543 528 5,100 540 524 5,100 531 515
5,200 543 537 5,200 539 534 5,200 530 524
5,300 541 546 5,300 538 542 5,300 530 535
5,400 539 554 5,400 537 552 5,400 530 545
5,500 537 562 5,500 535 560 5,500 528 553
5,600 534 569 5,600 532 567 5,600 525 560
5,700 531 576 5,700 528 573 5,700 523 567
5,800 527 582 5,800 525 580 5,800 520 574
5,900 524 588 5,900 522 586 5,900 517 581
6,000 519 593 6,000 517 590 6,000 513 586
6,100 514 597 6,100 513 595 6,100 508 590
6,200 508 600 6,200 508 599 6,200 503 594
6,300 502 602 6,300 502 602 6,300 499 598
6,400 497 605 6,400 496 605 6,400 494 602
6,500 490 606 6,500 490 607 6,500 489 605
6,600 483 607 6,600 484 609 6,600 483 607
6,700 476 607 6,700 476 607 6,700 477 608
6,800 469 607 6,800 459 595 6,800 468 605
6,900 459 603 6,900 444 584 6,900 453 595
7,000 445 594 7,000 434 579 7,000 441 587
7,100 437 591 7,100 425 574 7,100 428 579
SOURCE
Coast High Performance
1650 W. 228th St.
Torrance
CA  90501
310-784-2977
www.coasthigh.com
Federal Mogul (Fel-Pro Gaskets)
N/A
federal-mogul.com
COMP Cams Westech Performance Group
11098 Venture Dr., Unit C
Mira Loma
CA  91752
9-09/-685-4767
www.westechperformance.com
Dart Machinery
353 Oliver St.
Troy
MI  48084
248-362-1188
www.dartheads.com
  • «
  • |
  • 1
  • |
  • 2
  • |
  • 3
  • |
  • 4
  • |
  • 5
  • |
  • View Full Article