Nothing defines the personality of a performance engine quite like the camshaft. From the power to the operating range, and even the curbside bark at idle, the cam sets the tone. With the appropriate cast of supporting components, including the heads, induction, and compression, you can generally expect more peak power as the camshaft is stepped up. On the flip side, those long-duration numbers loathe low-rpm operation, snuffing idle vacuum and driveability. Here lies the classic trade-off in a dual-purpose performance machine—determining how much cam is enough and how much is too much. If your plans are easy street cruising in choked urban traffic, that line is quickly crossed. Contrarily, if max high rpm power with a lumpy boulevard idle announcing your presence is the aim, more cam is usually the word.
To get a handle on how this all plays out in a real-world engine combination we decided to hit the dyno with three hydraulic roller grinds from Crane Cams. Our test engine is nothing more exotic than a production big-block Chevy 454. The engine was prepped by boring it out for a set of short-dome JE pistons to bring the compression ratio over the 10:1 mark, adding a set of Scat H-beam rods for durability, while freshening the stock Chevy crank. Up top, we went with a set of deceptively capable oval-port AFR cylinder heads. The heads feature a modest port volume of just 265 cc, but these fully CNC-ported castings have the airflow to support healthy output. Supplying the air is an Edelbrock Performer RPM Air-Gap intake manifold fed by a Holley 950 Ultra HP 4150-series carburetor. In short, our engine is the type of budget performance Chevy big-block you’ll find on streets across the United States, based on production components and spiced up with aftermarket goodness where it counts.
With the popularity of hydraulic roller cams in today’s street builds, it made sense to select that cam configuration for our dyno session. The advantages of the juice roller include virtually eliminating unexpected cam lobe/lifter failure in initial running, and the ability to add enough valvespring reliably to spin up some high-rpm power. The roller profiles offer much more lift than we would expect to run reliably on a flat-tappet combination, giving the potential for serious power production. To complement the cam, we opted for a set of Crane’s standard retrofit hydraulic roller lifters, PN 13532-16, along with Crane’s excellent 13763TR-16 aluminum-bodied roller rocker arms. The cylinder heads were ordered with AFR’s excellent hydraulic roller spring combination, so we were covered there.
What difference does a cam make? To find out we lined up a trio of Crane hydraulic rollers
Our test engine is your basic street performance big-block Chevy 454, freshened with a set
Our baseline “big” cam—the smallest of the lot—is conservative by today’s performance stan
Cammed For Power
To best illustrate the varied characteristics affected by cam size, it made sense to step the specifications up fairly substantially between the cams. We opted for sizable jumps of 12 and 14 degrees duration as measured at .050-inch lift. Our baseline cam, with 222/230 degrees duration at .050 would be considered a baby cam by performance veterans, but with lift of .576/.598 inch, it moves the valves with authority, and with a healthy lope can in no way be construed as a stock cam. Testing showed that even this small stick has its big-boy pants on, taking our mild 454 combo up to 570 hp at 5,800 rpm, and pulling cleanly over 6,200 rpm.
That’s healthy power for a pump-gas street 454. What was more impressive came lower in the operating range, where the torque right off the hit at 3,000 rpm was 539 lb-ft, twisting strongly to a peak of 587 lb-ft from 3,900 to 4,100 rpm. Our small cam delivered the torque needed to launch heavy street metal, while dishing plenty of punch up top. While the duration specs would seem conservative, don’t be fooled, this unit definitely proved to be performance minded. The smallest of our trio of cams idled with a noticeable performance lope and registered a healthy 15 in-hg of vacuum at a 1,000-rpm idle.
Our next step in cam size moved up to 234/242 degrees duration at .050, a neighborhood that is popular with today’s street performance enthusiasts. We tore the engine down as it sat on the dyno for the cam change, retaining everything else exactly as it was in our previous combination. The upsized cam featured a significant jump in lift, shoving the valves to well over the .600-inch mark. We expected the increase in lift and duration to tap into more of the excellent high-lift airflow of the AFR heads, and bump top end power. The dyno numbers showed a textbook example of what is gained and what is lost as the cam timing is increased. Up top, we now recorded 599 hp at 6,100 rpm, gaining in both output and usable rpm, however, the bump of 12 hp up top shaved 8 lb-ft from peak torque, and shifted the torque peak higher up the rev range. This move in the torque curve was most noticeable in the lower end of the rev range, with substantial torque losses below 4,000 rpm. Idle lope was noticeably more pronounced and vacuum measured 12 in-hg at 1,000 rpm.
To run a hydraulic roller in a block originally designed for a flat tappet requires only a
Our AFR 265cc oval-port heads were equipped from AFR with their excellent hydraulic roller
Topping our Chevy big-block test engine is an Edelbrock Performer RPM Air-Gap intake and H
Here lies the classic trade-off in a dual-purpose performance machine —determining how much cam is enough and how much is too much.