But we don't want to muddy the waters too much here. This is a big cam for a 9:1 compression 350ci small-block. The key indicator here is idle vacuum, which measures a measly 7 inches at 850 rpm. This compares with more like 11 inches of vacuum with the milder hydraulic roller combination. What this max throttle dyno test doesn't illustrate is how crisp (or soggy) the engine would be at part throttle. While the idle vacuum numbers indicate a weak part throttle, the vacuum numbers are actually better than we anticipated given the cam's long duration numbers.
Frankly, we were hoping to see 430 with a cam change, which turned out to be optimistic. As it was, we saw a solid 19hp increase, and had we spent another couple of days flogging rocker ratios, lash changes, and perhaps a single-plane intake manifold, it's possible we could have achieved our goal.
ConclusionWith this test, we've now tested this same long-block combination with four different camshafts with the same heads, intake, and carburetor combination. The beauty of this is that you can see how the additional cam timing affects the power curve. Big cams basically move the torque curve up in the rpm band, hurting the bottom-end torque while improving top-end horsepower. It's as simple as that. But for a street engine that spends most of its time at part-throttle, a big cam may not always be the best choice. But with all these tests, you now have a better idea of the style of cam that is right for your next small-block buildup.
Power CurvesTest 1 is the maximum power generated last month using the GM Performance Parts Hot hydraulic roller cam and 1.6:1 GMPP roller rockers. This test also used an Edelbrock Performer RPM Air Gap intake, Holley 0-4779 750-cfm carburetor, an HEI distributor, a set of 151/48-inch Hedman headers, and a pair of 211/42-inch Borla Pro X/S mufflers.
For Test 2, we swapped in the custom Comp Cams 280/288 Street Roller, lifters, and rocker arms as well as a stronger MSD-6A ignition system with 36 degrees of total timing. The mechanical roller camshaft offered 22 degrees more duration at 0.050-inch tappet lift, which is why we lost torque below 3,600 rpm. Idle vacuum is 7 inches at 750 rpm.