Remember this little 318 from our May issue? This month our powerful supercharged small-bl
While the old adage that there's no replacement for displacement does have some truth to it, the fact is that there are many ways to make a small engine powerful using aftermarket parts, especially when you bolt on power-adders like nitrous oxide, a turbocharger, or supercharger. Deciding to show the potential of one of the smallest and most overlooked Mopar small-blocks, the 318, we teamed up with The Supercharger Store for a project with some specific goals in mind. Take a mild 318 built with quality internals, then supercharge and tune it to make 650 hp and 600 lb-ft of torque, run 12s, and get 16 mpg in an A-Body on 91 octane pump gas.
As you might remember from the first article in this series (May '10 issue), our .030-inch over 318 exceeded its horsepower goal, making 662.7 hp at 6,000 rpm, but fell just shy of the torque goal making a stout 587.5 lb-ft at peak. Even so, this engine should still easily propel a correctly prepared A-Body to sub-13 second quarter-mile elapsed times, and the brake specific fuel numbers indicate we'll be close to our mileage goal as well. To find out how this engine will perform in the real world, we prepped a test-mule '73 Plymouth Scamp for the 318.
Originally equipped with a Slant Six, power steering, air conditioning, and a column shifted automatic, we decided to retain all of the factory options and add power brakes as well. One benefit of this project is that since a supercharged engine doesn't require a radical camshaft to make power, we'll have plenty of manifold vacuum for power brakes. Calling Master Power Brakes, we ordered a power disc brake conversion kit for the front and a set of 11-inch drums for the 8-3/4 rear end we'll be installing. We've always been impressed with the quality and fit of Master Power's products, and this project was no exception.
To handle the nearly 600 lb-ft of torque this little monster makes, an 8-3/4 rear differential was the logical choice, and 3.23 gears were chosen for drivability and economy. To hang the rear end, we chose a set of Mopar Performance super stock springs, installed with offset brackets and hangers to make the most room for big rear tires. Goal 45 Motorsports fabricated the frame connectors, and we installed an adjustable pinion snubber to minimize axle wrapup. After serving the front suspension, we installed a set of Pacer wheels with 275/60R15 rear Mickey Thompson street radials and front P16580R15 tires, all from Competition Tire.
With the suspension ready, we called Pro Trans who built a fully automatic 727 TorqueFlite that would stand up to our 318's torque. We even maintained the factory column shifter, using a Lokar kick-down cable system in place of the factory kick-down linkage. Knowing that we'd have to compromise in terms of the torque converter in order to achieve our mileage and performance goals, Alan at A-1 Performance built us a somewhat tight 3,000-rpm converter for our application.
One of the most important systems in a supercharged application is the fuel delivery system, as the engine's appetite changes dramatically throughout the rpm range. We chose a MagnaFuel Protuner 525 fuel injection fuel pump, inline filter, and boost-referenced fuel pressure regulator to provide the necessary go juice for our application, knowing these parts are proven and reliable. To build the special blow-through carburetor, we called Bob Oliver at Competition Carburetion. Like the converter, the carb for our application will be a bit of a compromise, blending good power with minimal fuel consumption.