We’re on the Autobahn Country Club’s South Track in Joliet, Illinois. In the passenger seat is Justin Fouts, from Fall-Line’s marketing department, who had earlier shown me the proper lines around the track’s mixture of 15 turns. After a tight first corner, the track unfurls into a series of left and right sweepers that increase in speed until a tricky, chicane-like turn 9-and-10 combo separates the layout’s two high-speed sectors.

With some heat into the tires and brakes, I start to step more deeply into the throttle. There’s some slight hesitation when I first get into it, which may have been some bad gas, but the engine fought through it to send the meter on the digital dash shooting towards redline. Although torque is abundant, horsepower made through high revs is where the engine thrives. And because it’s utilizing Fall-Line’s shorter 4.10 differential, running through the gears happens just that much more quickly.

The car turns in sharply and the Yokohama slicks hang on tenaciously. The ride is racecar-stiff with the Moton Club Sports coilovers. The Brembo brakes (355mm slotted discs and four-piston calipers in front, 345mm slotted discs and four-piston calipers in back, Cobalt pads all around) wipe off speed with instant bite and seem to have plenty in reserve. Although I didn’t approach the limits in my few short laps, it was easy to tell that Fall-Line had dialed the car in beautifully. It responded to every input, be it brakes or steering, with direct, linear feedback. I’m sure there were some frightening levels of grip left on the table.

Lapping the same track in the 3D Design Z4 couldn’t have been more different. Set up for the street and retaining all of its sound deadening materials, the car attacks the straights with a restrained whoosh of spooling turbos and the subtle snarl of the Eisenmann exhaust.

Midrange torque seemed to be the dominant characteristic, as with all N54 engines. This particular car’s ECU uses an ESS Tuning Stage 2 program that the company says is good for an extra 90 hp and 70 lb-ft of torque, for a total of 390 hp and 370 lb-ft. As it’s still a work in progress, the car is expecting a bigger, more-efficient intercooler.

Like other N54 engines, the little stock turbos start to run out of breath near the redline. Up to that point, the car surges through the gears effortlessly. There was enough power down low to get the back tires to slip coming out of the tighter turns before traction control spoiled the party. The power down the straights was impressive and it wouldn’t surprise me if we were hitting top speeds similar to its carbon-bodied E85 brother. But all that power made the brakes seem like the weakest link as they started to fade. More aggressive brake pads might be able to make up for that.

The car sits on a rare set of M3 GTS wheels known as BBS Motorsports GT4 RE. They were brought in by 3D Design North America’s sister company, WheelSTO, and are wound with Yokohama Advan S-Drive tires. KW Variant 3 coilovers take care of the damping duties. 3D Design also had a company out of the Chicago area called IND Distribution take out the height adjustment collar to get the car to sit an extra half an inch lower in back. Dinan camber plates help tilt the front wheels in to clear the fenders and give it some extra turn-in.

The car eagerly attacked every corner it was thrown into and you could feel the front tires starting to slip before the rear started to rotate to get the balance back towards neutral. Then it was just a matter of feeding in the right amount of throttle. And even when the fading brakes meant that the corner had to be taken faster than desired, the car responded well to trailing brakes into the corner.

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