The 4.0L Whipple supercharger and LSX376 B15 crate motor from Chevrolet Performance seemed like a match made in heaven, and we had the dyno sheets to prove it, so why keep going? Does anyone really need more than 900 hp in a street car? Probably not, but just because we managed to exceed 900 hp so quickly doesn't mean we were done with this amazing little crate motor and supercharger combination. We'd like to try turbos or nitrous—maybe both—but a blower is an easier install for the weekend warrior, so we're sticking with this configuration for now and trying to maximize the power potential lurking within all these parts. We don't mind taking things to the next level here at Car Craft. We look at an engine not for what it is, but rather for what it could be, and something many enthusiasts don't realize is that there's a way to make more power with less boost by using a bigger cam.
LS motors (especially the rec-port LS3 variety) respond amazingly well to cam changes because they already sport sufficient displacement, compression, and head flow. Wilder cam timing is all that's needed to complete the performance package, and it's not uncommon for a cam swap to net 60–70 hp on a typical LS3. We were wondering if the same holds true in a boosted application. Luckily, we had the perfect test mule to answer just such a question. This article compares two factory blower cams (LSA and LS9) to a Comp blower cam from Brian Tooley Racing. We also threw in an off-the-shelf, normally aspirated grind that matched the specs of the blower cam but had a much tighter lobe-separation angle (LSA). This comparison would illustrate the difference between cams designed for normally aspirated and supercharged applications. In addition to power and torque, we also monitored boost pressure to illustrate the theory that when it comes to cam timing, you can get more power with less boost. The B15 crate motor was still sporting the 4.0L Whipple twin-screw supercharger, but we dialed it down for this test with the installation of a 4.75-inch blower pulley because there's no need to set things on kill for a simple cam test. This pulley combination dropped boost to a bit more than 16 psi at 6,200 rpm with the LS9 cam supplied with the crate motor.
The high-lift blower and NA cams also required upgrading the valvesprings. In addition to the blower cam, Brian Tooley Racing supplied one of its 0.660-lift Platinum spring packages that contained everything needed for the swap, including titanium retainers. The combination was dialed in using a Holley HP EFI system and 83-pound injectors.
Beginning with the LS9 cam supplied with the motor and run through 17⁄8-inch headers from American Racing, the supercharged LSX produced peak numbers of 735 hp at 6,200 rpm and 664 lb-ft at 4,600 rpm. There was more power to be had at higher engine speeds, but we limited the testing to 6,200 rpm, where the supercharger/cam combo produced 16.2 psi.
To get a clear picture of what cams had to offer the supercharged LSX376 B15 crate motor, we ran no less than four different cam profiles: two production cams and two from Comp Cams.
The LS3-based crate motor featured an LSX iron block stuffed with a forged rotating assembly and as-cast LSX heads.
To maximize airflow, the 4.0L Whipple supercharger was configured to accept a 105mm (Ford) Accufab throttle body.
Since we weren’t testing for ultimate horsepower, we installed the largest (4.75-inch) blower pulley in our arsenal to minimize the boost pressure during the cam test. Equipped with this pulley and the LS9 cam, the supercharged LSX produced just over 16 psi at 6,200 rpm (we also limited engine speed).