Remember the orange '70 Challenger that we brought you in last July's Mopar Muscle that combined 21st century technology with the E-Body's late-20th century style? The one that left you wondering how its builder could improve on it . . . or top it?

Well, XV Motorsports topped it with a drop-top Dodge based on one of the rarest Mopars ever made-the '71 Challenger convertible, of which fewer than 2,200 were made.

A collector, who already had potent machinery in his garage, such as a Hemi-powered Superbird, a V-code '70 GTX, and an M-code '69 Barracuda, as well as nearly a dozen examples of American muscle and world-class exotica, wanted something like them, but different. "He approached us and told us he wanted to do a convertible," says John Buscema, president of XV Motorsports. "I told him that we had a '71 Challenger. I showed him the body style, and he really liked it, so he had it built."

John says, "The '71's engine is a heavily worked, 600hp, 6.1-liter Hemi." A T-56 six-speed was upgraded with triple-cone synchronizers for higher-rpm shifts, and a dual-disc hydraulic clutch went in place but not without some significant fabrication. "To put that tranny in requires reworking the transmission tunnel to fit a T-56, so we had to fabricate a new transmission tunnel," John says. Out back, there's a 4.33-geared, 8-3/4-inch rearend that works great with the T-56. "The reason we were able to do that and still have it usable is because the final drive ratio on a Viper T-56 is around 0.50:1," he points out, while noting that first through fourth are geared 2.66, 1.78, 1.30, and 1.00. "You have two overdriven gears: fifth and sixth. fifth is 0.74 and sixth is 0.50, which is great. it's all close-ratio,so you can run a lot of gear in the back of the car."

You can also run a lot of tire in the car. There are big Michelin Pilot Sports at each corner (335/30YR18s in back and 275/35YR18s in front), wrapped around a set of 18-inch, Kinesis-forged, three-piece wheels. They fit thanks to a little fender-lip rolling and XV's own Level II suspension system. The XV suspension replaced the OEM torsion bars/rear leafs with hardware fabricated in-house. The '71's chassis features two aluminum A-arms, aluminum high-pressure monotube coilovers, and aluminum spindles on each side in front, with a power rack-and-pinion steering system, custom front antiroll bar, and adjustable bumpsteer kit-all surrounding an aluminum K-member that cradles the powertrain while adding strength and subtracting weight. In back, there's a three-link suspension that features billet aluminum lower links, an adjustable Panhard rod, and aluminum monotube coilovers, with a custom rear antiroll bar for good measure. And for another good measure, there's XV's Level II brake package, with 14-inch rotors and six-piston calipers in front and 13-inch rotors/dual-piston calipers in back.

XV's fabrication shop also made additional structural reinforcements that went into the Challenger's body. "If you're familiar with the chassis stiffening that we do, this car has an additional piece in it that we put on convertibles," John says. "There are four pieces that we put in the car for chassis stiffening. In the convertibles, there's a fifth piece that we use on the framerails in the back." They also made a set of billet/hydraulic aluminum hood hinges for this car, which will likely join XV's product line soon.

The interior got as much attention as the chassis, with a prototype center console containing an Alpine audio system, flanked by two custom-upholstered Recaro bucket seats. A complete custom gauge cluster, including a 200-mph speedometer and 10,000-rpm tach, replaced the stock pieces. blue leather covers the seats, doors, and side panels.