To those interested in power output, nothing has the attraction of a supercharger. Forcing atmosphere into an engine makes it take a charge out of proportion to its displacement, and with that, produce power out of proportion to its size. There are many types of supercharger systems used in automotive applications, from turbos, to positive displacement Roots-style blowers, to belt-driven centrifugals. Each has its pros and cons, with turbos getting a nod for efficiency but often presenting an installation nightmare. Traditional Roots blowers are capable of effective low-rpm boost, though they are too ostentatious for some and are no lightweights. Belt-driven centrifugal blowers have become very popular for several reasons. The systems are relatively easy to install, offer increasing boost with rpm, and the bottom line is they make serious power.
The leader in Mopar centrifugal blowers is a company called The Supercharger Store. We had looked longingly at some of its well-designed products at various Mopar events for several years now, and decided to finally take the plunge into the realm of boosted power. The Supercharger Store systems are based on the ATI Procharger line of blower units, superchargers that are well-proven in drag racing and street applications. Most of the ATI blowers are fully self contained, meaning that they carry their own internal lubrication supply, eliminating the need for plumbing pressure and return lines between the blower and the engine. The Supercharger Store has many variations of blower systems and components specifically for Mopar applications, so we had many options to consider when formulating a plan for a blown big-block Mopar.
Popular kits are based on blowers of various capacities, depending upon the boost level and power objectives. Initially we were going to go with a basic street kit, built around the 1,400-cfm D1SC Procharger. Later, we reconsidered the project and settled upon the much larger capacity F1-R, a hotter version of the 1525-cfm F1, rated for 2,000 cfm. This unit would be enough to easily produce high boost in a 440 cubic-inch engine, and yet have the capacity to handle the greater needs of a high-output stroker combination if we later choose to go that route. Boost pressure is dependent upon sizing as well as rpm, and the rpm can be adjusted within the unit's operating range by the selection of blower pulleys. Our intention was to use the F1-R on a typical bracket race/street-style 440, and spin it for high boost. Our engine makes peak power naturally aspirated at roughly 6,000 rpm, with a redline of 6,700 rpm, so those points are established. The drive pulley ratio can be determined by the operating rpm range, the displacement, and the targeted boost. The Supercharger Store has the data to match sizing for the required goals.
Engine ModsOur prospective blown engine was typical of a hot street or strip 440, built on a .030-inch-over factory block, with 10.3:1 compression, Edelbrock heads, and a COMP solid lifter cam. The engine produced a best of 550 hp on the dyno, a very respectable number for a relatively inexpensive and simple combination. This engine would serve to be a testbed of the Procharger's potential, but we needed to make a few changes to prep it for blower duty, besides simply bolting on the blower. We intended to run fairly high boost levels, at which the engine's 10.3:1 compression ratio would be too high, especially on pump gas. To get the ratio closer to the 8:1 ratio recommended by The Supercharger Store, we needed to take a good two points of compression out. A piston change is the obvious solution, but we already had a fine running 440 bottom end, and were not too eager to tear it down and toss out the pistons in favor of custom dished replacements. Our goal was simply to evaluate the power potential of the blower system on the dyno. Weighing everything involved, including the full teardown and replacing the pistons, and then re-balancing the short-block, we weren't too far from building a new short-block.
We found the solution from a company called Flatout Gaskets, makers of unique rubber-coated copper head gaskets, among other sealing products. We had used a set of these copper gaskets in another buildup, and were impressed that they sealed both compression and fluids perfectly, without the aid of O-rings or additional sealant. Flatout manufactures these gaskets in a wide variety of thicknesses, including a 0.125-inch-thick version that can be used as a cylinder head spacer, in conjunction with conventional gaskets. This spacer would add over 30 cc of volume to our combination, enough to drop the compression ratio to 8:1. To aid in the cylinder head clamping, the headbolts were replaced with a set of Milodon head studs. Another point to consider was to ensure the cylinder head alignment dowels in the heads were sufficiently long to accommodate the thick gasket pack. We ended up replacing the dowels in our engine.