Supercharged Chevy Small Block - Boosted Bumpsticks

We Compare Cams On A Blown & N/A Small-Block.

Richard Holdener Aug 1, 2009 0 Comment(s)
Sucp_0908_07_z Supercharged_chevy_small_block Comp_cam 2/26

Our test centered on a pair of Comp Xtreme Energy cams (XR282HR shown). The idea was to illustrate the differences offered by the pair in both normally aspirated and supercharged configuration. The XR258HR offered a 0.480/0.487 lift split, a 206/212 duration split and a 110-degree lobe separation angle. The larger XR282Hr cam featured a 0.510/0.520 lift split, a 230/236 duration split and the same 110-degree lobe separation angle.

Before running, our test mule required some minor work. The first order of business was boost. The super for our supercharged mill came from Vortech Engineering in the form of its Universal Carbureted small-block kit. Originally designed for a blow-through carbureted application, we used this system with electronic fuel injection. This was a simple matter of running an Edelbrock Victor Jr. intake that had been retrofitted with a set of injector bungs. Use of the converted carbureted intake allowed us to bolt on the carburetor enclosure and 4-hole throttle body from Accufab.

Unfortunately, interference between the fuel rails and bottom of the carb enclosure necessitated that we run a 2-inch carb spacer. This change further necessitated the use of an additional spacer to properly locate the junction between the discharge of the V1, S-trim supercharger and the inlet elbow for the carb enclosure. Once again, it was Accufab to the rescue in the form of a 90mm EGR spacer for a 5.0L Ford. Since the bolt holes and 90mm opening matched the Vortech enclosure already, all that was necessary was to mill the spacer to the proper thickness (1.23 inches). With the spacer in place, everything lined up and we were in business.

The (now) aluminum-headed L98 was run with an MSD distributor, a set of 1.75-inch dyno headers and the FAST XFI engine management system. Also present was a set of 36-pound injectors, which were a tad on the small side for our supercharged motor, but we managed to just sneak by using 50 psi of fuel pressure. The first order of business was to run the motor with the XR258HR cam in normally aspirated trim. Equipped with the Pro Comp aluminum heads, converted Victor Jr. EFI intake and XR258HR cam, the 350 produced 358 hp at 5,400 rpm and 396 lb-ft at 3,800 rpm. Torque production exceeded 375 lb-ft from 3,000 rpm to 4,900 rpm, but power fell off rapidly after 5,500 rpm.

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The impeller was an ultra-efficient curved-vein design that maximized both flow and response rate.

After the N/A runs, we added boost from the Vortech supercharger. The blower was equipped with a 3.33-inch blower pulley spun by a 6.0-inch crank pulley. Fed through the carburetor enclosure, the Vortech produced a peak boost pressure of 9 psi at 6,200 rpm. Equipped with the blower, the motor produced 454 hp at 6,200 rpm and 450 lb-ft of torque at 4,500 rpm.

After running few back-up runs, we tore into the engine to replace the XR258HR cam with the wilder XR282HR grind. Off came the induction system, rockers and pushrods, followed by the front cover, timing chain and Xtreme Energy cam. The XR282HR cam was run with the factory lifters. After everything was buttoned back up, we ran the combination in normally aspirated trim. Equipped with the larger XR282HR cam, the motor produced 407 hp at 5,800 rpm and 405 lb-ft at 4,000 rpm. This represented a jump of nearly 50 hp over the smaller cam. While the smaller cam offered more torque up to 3,500 rpm, the larger cam pulled away thereafter.

Adding the blower to the equation really showed the worth of the larger cam. Running the XR282HR cam increased the peak power numbers to 561 hp at 6,200 rpm and 501 lb-ft at 5,000 rpm. Oddly enough, the peak boost dropped down from 9 psi to 8.1 psi--a sure sign that the breathing potential of the motor had improved.

Comparing the results, we see that the cam change offered a gain of roughly 50 hp in normally aspirated trim, but over 100 hp once we added boost. It is also important to point out that the while the smaller cam improved torque production below 3,500 rpm in normally aspirated trim, this situation changed once we added the blower. Even down at 3,000 rpm, the larger cam made more power than the smaller one when equipped with the supercharger. Naturally all testing was run with the same blower and crank pulleys, the same timing and air/fuel ratios as well as the same air and water temperatures. This test illustrated that not only do forced induction motors tolerate wilder cam timing, but they (in fact) thrive with the right cam specs.




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