Words and Photos: Richard Holdener
There is a very famous saying among performance enthusiasts that goes something like this: No matter how much power you give someone, they will always want more! This is especially true of racers, but even applies to hardcore street guys. The problem is that once we have sampled what feels like all the power we will ever need, that level becomes commonplace, and we eventually find ourselves looking for ways to add even more.
Even when you start with something already plenty potent, like a big block Chevy, there will come a time when even the grunt supplied by an overabundance of displacement will start to feel inadequate. It is with this in mind that we set out to build a combination that already had a few extra helpings of MORE built right in. Now toss in the ability for future growth, and it’s easy to see why a blown big block has so much going for it. There is just something about the combination of cubic inches and pressurized pounds that gets the old adrenaline pumping.
With MORE in mind, we decided to toss cams, cubes, and compression at the build even before adding boost. To get things started, we immediately increased the displacement of the test motor. Though we started off with plenty, the Gen V 454 was punched out to 496 cubic inches thanks to the combination of a 4.25-inch Scat stroker crank and .060-over forged pistons from CP-Carrillo. The 4-bolt block was properly machined to receive the 4340 forged crank, 6.385-inch forged rods, and small-dome forged CP forged pistons. The combination of the forged internals produced a stout short block more than ready for the application of boost. The stroker was finished off with a blower-specific camshaft and solid roller lifters from COMP Cams. The 300BR-14 featured .652 lift (intake and exhaust), a 255/262-degree duration split, and blower-friendly 114-degree lsa.
Since the motor was now sporting more cubic inches, we decided it needed more airflow. To supply (actually exceed) the necessary flow requirements, we installed a set of CNC-ported BBC heads from ProMaxx. Though ProMaxx offered a number of different BBC heads to choose from, including larger 370cc intake runners, we opted for the CNC-ported, 340cc versions. As supplied by ProMaxx, the heads featured a 2.30/1.88 stainless (back-cut and swirl polished) valve combo, 122cc combustion chambers, and intake ports that topped the magic 400 cfm (peaks of 412 cfm at .900 lift). The ProMaxx heads came equipped with a triple spring package designed to support a roller cam of up to .900 lift — more than enough for our .652-lift roller. The heads were installed using Fel Pro head gaskets and ARP head studs.
The valves were actuated using a set of 1.73-ratio Crane Gold roller rockers and hardened pushrods from COMP Cams. All of this was initially topped with an Edelbrock Super Victor intake and Holley 1050 Ultra Dominator carb. After a few break-in cycles, the normally aspirated 496 produced 676 HP at 6,400 RPM and 591 lb-ft of torque at 5,300 RPM.
With the baseline numbers out of the way, it was time for boost. For our stroker, boost was supplied by a 6-71 supercharger kit supplied by Speedmaster. The highlight of the Speedmaster kit was the 6-71 supercharger from the Blower Shop, but the kit also included all the necessary components, including the dedicated lower intake, the blower, and crank pulley and belt tensioner assembly. Off came the Edelbrock intake and on went the blower manifold, followed by the blower, carb adapter, and dual Holley 950 HP carbs. The blower-specific carbs were designed for use with the 6-71 and featured manifold-referenced power valves. Designed for use on the blower, the carbs worked well at WOT right out of the box, though we did have to juggle (remove) primary and (add) secondary jetting to dial in the cruise mixture.
The blower was initially set up with a 50-tooth crank pulley and a 55-tooth blower pulley, meaning the blower was under driven by 10 percent. This resulted in a peak boost of 3.3 psi, where the supercharged stroker produced 809 HP and 686 lb-ft of torque. After reversing the pulley combo, the result with the blower spun 10 percent over driven was a peak boost of 6.8 psi. The jump in boost increased the power output by over 100 HP, to a peak of 928 HP and 790 lb-ft of torque. While that might seem like enough power for most enthusiasts, there is definitely room to grow if you decide you want more!
Graph: 496 BBC-NA vs Speedmaster 6-71 Blower (3.3 & 6.8 psi)
As we have come to expect from the installation of a hefty supercharger on a big block, the 6-71 kit from Speedmaster improved the power output substantially. The already stout NA combination produced 676 HP and 591 lb-ft of torque, but that jumped to 809 HP and 686 lb-ft at just 3.3 psi after installation of the supercharger. Reversing the pulley combination from 10 percent under driven (50 crank/55 blower) to 10 percent over driven (55 crank/50 blower) increased the blower speed and upped the peak boost pressure from 3.3 psi to 6.8 psi. This resulted in an increase in power from 809 HP and 686 lb-ft to 928 HP and 790 lb-ft. The extra 3.5 psi increased the power output by 119 HP.