Dyno - Tested Camsheft Theory

Hydraulic Flat-Tappet vs. Mechanical Roller
This test originally appeared in our November '00 issue with the plan to pit a typical flat-tappet hydraulic cam against a more aggressive mechanical roller. While most car crafters will recognize that this is anything but a fair fight, the concept was not to see who wins, but rather how much of a difference the mechanical roller cam is worth. The follow-up question then becomes, is the gain worth the additional price of the roller? The guinea pig for this test was a Steve Dulcich-built 440ci Mopar using a set of ported mid-'70s 742 iron castings, a Mopar Performance M-1 intake, an 850-cfm Barry Grant Speed Demon carb, and a set of 178-inch Hooker headers flowing through a pair of Flowmaster mufflers.

The difficulty with doing this story is coming up with a fair comparison, which in reality is not easy because the mechanical cam has lash figures of 0.016 and 0.018 inch, which do not allow comparing advertised duration at, say, 0.006-inch of tappet lift. The duration-at-0.050 numbers indicate that the mechanical roller is much "bigger" but most of that is inherent in the roller design, the exact concept this test was intended to evaluate. The included cam-specs chart indicates how much more aggressive the mechanical roller cam is merely by evaluating the differences in valve lift. The mechanical roller comes in with almost 0.070 inch more max valve lift that certainly contributes to the significant power increase inherent with a mechanical roller cam.

Is this truly a fair test? We'll let you decide. A concrete result of this apple-to-oranges comparison is that the roller cranked out over 20 lb-ft and 20 hp more average power with a peak horsepower difference well over 60 hp. Those are numbers that are hard to ignore as long as your wallet can accommodate the price of admission. END

You really can't judge a cam just by looking at the lobes. Roller lobes benefit from allowing very high ramp speeds so the lobe can push the valve open at a faster rate to generate more lobe lift than a flat-tappet cam.

DYNO DATA Hydraulic Roller DifferenceRPM TQ HP

TQ HP TQ HP3,400 472 306 469 304 -3

-23,600 484 332 485 333 1 13,800 496 359

498 361 2 24,000 500 381 507 386 7 54

,200 501 401 512 410 11 94,400 503 422 516

432 13 104,600 502 440 520 455 18 154

,800 499 456 521 476 22 205,000 492 469

521 496 29 275,200 483 478 513 508 30

305,400 469 482 505 519 36 375,600 453

483 492 525 39 425,800 434 480 479 528

45 486,000 416 476 463 529 47 536,200

393 464 445 526 52 626,400 -- -- 426