The Replacement For Displacement Part 2

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.

To ensure proper ignition and expulsion of the spent fumes, we called on MSD and TTI respectively. TTI is known for quality exhaust components, and they recommended their off-the-shelf step headers and 3-inch exhaust system. MSD provided the Blaster coil, plug wires, 6AL ignition box, and billet distributor to ensure our boosted mixture ignites at the proper time. To further control detonation, we also installed a water injection system from The Supercharger Store. This system uses distilled water to keep the intake temperature at 80 degrees Fahrenheit, and the water slows the flame front as well, effectively increasing the octane of the fuel.

Since our Scamp was shaping up to be a real performer, we decided to make it look its best as well. Taking the car to Goal 45 Motorsports, we ordered two Chrysler colors, Inferno Red and Cool Vanilla, from local M&M Paint, then applied the two-tone paintjob in their booth. Alejandres Upholstery stitched up the interior to match the outside of the car, and we had the windows tinted as well.

Though our goal was to have Bob and the crew from The Supercharger Store drive the Scamp to the Mopars at the Strip show in Vegas, we just barely got it put together in time, finishing the car the night before they had to leave. Since there was no time for any shakedown passes or even to put some miles on the car, we decided not to risk it and took it to the show on the trailer. At the show, the car was driven regularly, performing great on the street. The one pass we got to put on the car in Vegas yielded a 13.2 second elapsed time at 109 mph which isn't bad, but is a little shy of our goal.

After the Vegas show we put about 300 miles on the car and performed a little carb tuning. Taking the Scamp back to the track yielded best of 13.6 seconds in the quarter-mile at 114 mph. Knowing that the car's mph reflected plenty of power to run 12s in the quarter, we knew the problem was with our sixty foot times. In our attempt to achieve fuel economy, our 3.23 rear gear ratio, combined with 27-inch-tall tires and a tight converter, just wasn't letting the car launch. Changing to a 3.91 gear, we went back to the track and ran the quarter-mile in 12.7 seconds at 118 mph, verifying our combination could go 12s with relative ease.

Overall, we're impressed with the performance of this combination. The car drives nicely, idles at 700 rpm with some 12 inches of manifold vacuum, and everything fits under the stock hood. With the 3.23 gears, we can easily cruise 75 mph at a relatively low 2,900 rpm. At those speeds, the car got an impressive 16.2 mpg, with plenty of power throughout the rpm range. Additionally, our performance goals were originally based on a 3,400-pound car, and as raced our Scamp tips the scales at some 3,650 pounds with driver. When you consider that this is an air-conditioned street car that comfortably cruises to the track and runs 12s, the performance of this 318 is unquestionable. As is, this combination is a viable alternative to the stroker big-block or Hemi engine, and with a little development would be nothing less than wicked.