Ford Mustang 5.0 Kenne Bell Cam Combos Comparison

This physical size combined with the difference in operating speed produces dramatically different efficiencies and power curves. A positive displacement supercharger usually provides near-instant boost production and a ton of low-speed torque along with it. The high-rpm nature of a centrifugal supercharger means it is best at supplying big horsepower increases. The trade off for all that top-end efficiency is less than ideal low-rpm boost production. The typical boost curve on a properly sized positive displacement supercharger is a straight line. As soon as the throttle is mashed, the blower provides peak boost and should be able to carry it all the way to redline. Such was the case during our cam tests. Centrifugal superchargers tend to make boost and power in relation to engine speed, with power coming on hard in the mid-range and especially at the top end. Boost for boost, the centrifugal will make more power due to its inherent efficiency (being a true compressor). The positive displacement supercharger however, will almost always provide more average torque throughout the rev range. Does this difference in efficiency and power production dictate different cam timing? That's what we aimed to find out.

The best way to find out what cam profile works well with a positive displacement supercharger is to try a few. That's exactly what we did here at MM&FF. The first step in our cam testing was to build a suitable test motor. There is obviously no "ideal" test motor, but we did want one that was representative of what might be found in a typical street Mustang. To that end, we built a 302 capable of withstanding the rigors of forced induction, without going overboard on the buildup. The basis of our test motor was nothing more exotic than a simple 5.0 short-block. Why not start with what nearly everyone else already has in their Mustang? This early 5.0 short-block was equipped with factory forged pistons. These pistons were notched in anticipation of the high-lift Xtreme Energy cams and larger-than-stock valve sizes in our aftermarket cylinder heads. Other than the valve reliefs, the short-block was kept bone stock.

Knowing that we planned to run a pair of cams offering well over .500 lift, we opted to install a set of free-flowing cylinder heads that could take advantage of the additional cam lift. Though many different heads are available for the 302, we chose a set of AFR 185 heads for our test motor. We have had excellent results with these AFR heads in previous tests and wanted to maximize the airflow potential of our supercharged test motor. The AFR 185 heads were installed on the awaiting short-bock using a set of Fel Pro 1011-2 head gaskets and ARP (7/16) head studs. Head studs are a good idea when running any type of forced induction. Topping the AFR 185 aluminum heads was an Extrude-Hone ported GT-40 lower intake. Since the Kenne Bell supercharger kit employed a dedicated upper intake casting, no GT-40 upper was necessary.

The centerpiece of our positive displacement supercharged test motor was the Kenne Bell (Autorotor) supercharger. Though the blower kits come complete, we opted for a few upgrades for our test motor. The first upgrade was the supercharger itself. Instead of the standard 1.5 1500, we installed the larger 2.2 Blowzilla supercharger. This Blowzilla offered 50 percent more power potential than the standard 1500. Since we expected the supercharger motor to exceed 400 hp, we wanted to make sure we had enough supercharger to properly test the cams. In addition to the Blowzilla blower, we also installed the Flowzilla inlet manifold. Not wanting to restrict the breathing of our test motor, we employed one of the new Kenne Bell inlet castings to minimize restrictions. In previous tests, the Flowzilla has been shown to be worth as much as 40 hp over the standard inlet casting. The combination of Blowzilla and Flowzilla gave us plenty of power potential.

The larger inlet manifold also allowed us to run a 90mm throttle body, as the inlet was machined to accept the big-bore throttle body. We employed a billet version from AccuFab for our testing. Additional intake mods included a 77mm mass air meter from Pro-M. The meter was calibrated for the 36-lbs./hr. injectors sourced from RC Engineering. The 36-pound injectors were good for over 500 horsepower, or more than enough for our test motor. In addition to the recalibrated meter and larger injectors, we employed an adjustable fuel pressure regulator and custom chip from Kenne Bell to meet our fuel and timing needs. After setting the billet MSD distributor at 8 degrees initial timing and making minor adjustments to the static fuel pressure, the motor ran perfectly every pass. The final performance component was a set of 15/8-inch Hooker long-tube headers feeding a pair of 3-inch exhaust pipes and Flowmaster mufflers. With everything finally hooked up, we were ready to test the supercharger combination with the stock H.O. cam.