Words and Photos: Richard Holdener

Okay people, here is the situation. We were fresh off a test where we upgraded a Gen VI 454 from the wrecking yard and couldn’t help but notice how perfect the combination was for boost. The 454 in question was a 1996-99 Gen VI 7.4L found in full-sized truck applications. A step up from the previous Gen V motor, the Gen VI featured higher compression, a hydraulic roller cam, and even revised fuel injection. The difference in power between the two generations was a significant 55 hp, but that was not our concern for this test. Starting with the Gen VI, we upgraded the combination with new heads, cam, and intake manifold. Using the Speedmaster oval-port, aluminum heads, COMP Xtreme Energy cams and a dual-plane intake, the power jumped all the way up to 469 hp at 5,600 rpm and 508 lb-ft of torque at 3,600 rpm. Equally important for our needs was the fact the aluminum heads not only improved head flow, but also reduced the static compression below 8.0:1. The extra power and lower compression produced a big-block just begging for boost!

Recognizing the new combination as an opportunity, we decided it was our duty to apply the much-needed boost. As luck would have it, Speedmaster recently introduced a new intake manifold for a BBC application designed to accept a 6-71 roots supercharger. In addition to the intake, they also offered blower pulleys, carb adapters, and a host of other goodies that when combined with the actual 6-71 supercharger, allowed us to add more than enough boost to our big block. The 6-71 itself came courtesy of the Blower Shop. The polished unit was capable of supporting way more power than our stock bottom end might withstand. Besides, all we were looking to do was add 6-7 psi of boost to our big-block (maybe a skosh more…okay, skosh and a half). We know from past experience that each pound of boost adds a sizable chunk of power, and who doesn’t love to see a blown big-block run on the dyno?

The Speedmaster components combined with the Blower Shop 6-71 made installation a snap. Adding the blower was no more difficult than a typical (albeit heavy) intake swap. The blower and ancillary components were combined with a pair of Holley 950 XP carbs (yeah, we know…over kill on isle two). With visions of Mad Max swirling in our heads, we installed the big blower onto the awaiting big-block. It bears mentioning the Speedmaster intake was actually designed not for our oval-port heads, but rather the larger, rectangular-port variety. Before you keyboard warriors (or port matchers) get too fired up, know that the mismatch did not stop the earth from turning nor did it likely (based on the dyno results) hurt power in any measurable way. The air found its way from the blower, through the manifold, and into the heads all on its own, even through that gauntlet of a mismatch, go figure. The final touch before running boost was to adjust the dual-quad, throttle linkage supplied by Holley.

With our blower installed and ready to run, it was time for some positive pressure. We used the Speedmaster cog pulleys to adjust the boost supplied by the 6-71, purposely starting under-driven and conservative with a 50-tooth crank pulley and 60-tooth blower pulley. So equipped, the 6-71 supplied a peak boost reading of just 4.1 psi, allowing the blown big-block to produce 545 hp and 527 lb-ft of torque. Stepping blower speed up slightly by replacing the crank pulley with a slightly larger 55-tooth version resulted in a jump in boost pressure to 5.5 psi. This pushed peak power to 587 hp and 564 lb-ft, while a 48/50 pulley combo netted 6.2 psi and 605 hp and 582 lb-ft of torque. Things were starting to get interesting. Swapping the position of the (still under-driven) 48/50 combo to an overdriven 50/48 resulted in 7.8 psi and 635 hp and 607 lb-ft of torque. The final run of the night saw a 55/50 pulley combo and a peak boost reading of 9.1 psi. This boost level produced 654 hp and 625 lb-ft of torque with over 600 lb-ft available from below 3,500 rpm out to 5,700 rpm. Blown big-blocks rule!

Equipped with aluminum (oval-port) heads and a dual-plane intake from Speedmaster, along with a COMP Xtreme Energy cam, the low-compression, Gen VI 454 produced 469 hp and 508 lb-ft of torque. After installation of the 6-71 supercharger, the peak numbers jumped to 587 hp and 564 lb-ft of torque at a peak boost reading of just 5.5 psi. The great thing about forced induction is the ability to increase power by cranking up the boost. A simple pulley change increased boost pressure from the supercharger to 9.1 psi, where the blown 454 produced 654 hp and 625 lb-ft of torque.

Sources: ARP, Arp-bolts.com; COMP Cams, compcams.com; Holley/Hooker/NOS, holley.com; MSD, Msdignition.com; Speedmaster, Speedmaster79.com