Big-Block Bumpstick Blowout

To get an idea of how cam size relates to output, the pros and cons, trade-offs and gains, we thought we'd see for ourselves how moving up or down the camshaft ladder affects an engine's output. We brought a GM Performance Parts HO 454 crate engine to Westech Performance Group's test facility in Southern California to do some testing. Our engine was based on a Gen V block, with a modest 8.6:1 compression ratio, topped with rectangular-port iron heads, and is rated at 425 hp. The only upgrade to the package was the addition of Edelbrock's excellent Performer RPM intake manifold, which we topped with an 850 Speed Demon carburetor. Along with the engine, we brought along a range of Comp's Xtreme Energy camshafts. We'll have a look at the power numbers, record the data, and we'll leave it up to you to decide which level of performance is right for your application.

We started with Comp's popular XE268 grind, a powerful street performance camshaft we have found to offer good driveability, even in daily-use applications with air conditioning and full accessories. This would be the baseline setup, with the plan being to step up the range from there, and gauge the effects. With the cam installed and run in on the dyno, we prepared for the test. The engine settled into a smooth idle at 850 rpm, with just enough grumble to distinguish the test engine as a performance mill. True to form, the XE268 showed very good output, posting 483 hp at 5,300 rpm, and 541 lb-ft of torque at 3,900 rpm. The relatively mild-mannered idle quality and excellent torque lower in the rpm range make the XE268 one of our favorite street grinds. The fast valve action produces output up top that would normally be seen only from a choppier, longer-duration cam of more conventional ramp rates. Testing on our 454 showed 15.7 inches Hg of manifold vacuum at idle, an exceptional level for an engine of this output. If the goal is getting the best of both worlds in a street and strip cam, the XE268 is one of our favorite choices.

In short order, we tore our test engine back down and stabbed in the next size up in the Comp XE line: the 274. The 274 adds 6 degrees of duration at 0.050 inch, bringing it up to 230 degrees. This level of duration is getting toward the edgy side for a true street machine, particularly in an otherwise stock car with an automatic and A/C. To get the most from this cam, an aftermarket higher-stall converter should be part of the program, though four-speed cars will be fine. As expected, the added duration resulted in a decline of idle vacuum, with our instrument now reading 12.4 inches Hg at the same 900-rpm idle. Power was up significantly, with output boosted to 507 hp at 5,700, though peak torque actually dropped slightly to 538 lb-ft at 4,000 rpm. Essentially, the result of the bigger cam was a shift in the torque curve, with a drop in torque in the rpm range below peak torque, and a corresponding gain in torque in the rpm range above.