After the sales success of the compact, front-drive-based CLA-Class sedan, Mercedes-Benz has migrated that car's platform into the hotter-selling compact crossover market with the GLA-Class, the GLA250 and the GLA45 AMG.

These crossovers largely mirror their sedan counterparts, but the CLA45 reflects unique changes due to the different dynamic of the taller body style and lessons already learned from the CLA45 and applied to the GLA45.

CLA45 has so far represented 5 to 6% of CLA-Class sales in the U.S., according to AMG Product Manager William Vetter. GLA's sales mix will likely be similar, he added.

As in the CLA45, the GLA45 has a 355-hp (265-kW), 332-lb·ft (245-N·m), turbocharged, 2.0-L four-cylinder engine driving all four wheels through a seven-speed dual-clutch transmission (DCT) front transaxle with a power take-off sending a maximum of 50% of the torque to the rear wheels through a two-piece driveshaft.

The engine's block is sand cast aluminum with Mercedes' Nanoslide cylinder-liner technology, and the crankshaft and pistons are forged for durability.

The BorgWarner dual-scroll turbocharger ducts two distinct exhaust streams from separate pairs of cylinders to the impeller with the aim of spooling up the turbo early to its 26.1-psi (1.8-bar) maximum boost. Exhaust exits through a larger 3-in (76-mm) diameter pipe that maintains that size all the way to the tip.

As with all AMG engines, the GLA45's four-cylinder is built by a single technician whose signature is on a plaque atop the engine. However, unlike previous AMG engines, this one is assembled at the company's Hungarian Kecskemet factory rather than at AMG's Affalterbach headquarters outside Stuttgart.

The engine's basic architecture represents one bank of the company's new AMG GT sports coupe unit, Vetter pointed out, indicating that engine's power potential. "You can imagine what we can do with the V8 if we want to," he said.

The GLA45 uses an active vane in the muffler to meter flow based on throttle position, engine speed, and load condition. This is a technology that will migrate to the S-Class and then proliferate through Mercedes' product families, said Vetter. The variability permits free flow of the exhaust gas and allows for an exciting sound, without punishing occupants while cruising on the highway at a steady speed, he said. "You can cruise in this without it being annoying."

The GLA45's electronic stability system features three driving modes to allow drivers more fun than the single mode of the GLA250's system. The modes are On, Sport Handling, and Off. Torque vectoring uses braking applied to the inside rear wheel to send more power to the outside rear wheel during aggressive cornering.

On is the regular mode, while the sport setting permits drivers more leeway in enthusiastic driving before intervening. Off actually means off, unlike some other systems that are only mostly off in that mode. The GLA45's Off mode, however does revert to On when the brakes are applied because in that case the driver isn't trying to add power and may be in a sticky situation that needs addressing.

The transaxle sends power rearward continuously. It is applied to the rear differential by a hydraulically controlled clutch pack. In regular driving, the clutch is disengaged, leaving the GLA in fuel-saving front-drive mode. When wheel slip is detected at the front, the clutch pack engages to send as much as half the engine's power to the rear wheels.

Like the stability control system, the transmission also has three driving modes: M for manual, S for sport, and C for controlled efficiency. In M and S modes, the engine management system coordinates with the transmission to retard ignition timing and suppress fuel injection under full load for faster shifts. Along with the open muffler vane, the intent is to provide a sporty sound on the upshift as we've heard with the raucous Jaguar F-Type's V8 engine. Drivers may debate among themselves the success of that sound when produced by a turbocharged four-cylinder engine.

The transmission features a race start function for maximum acceleration from a standing start, which contributes to the car's speedy 4.8-s 0-60 mph (0-97 km/h) acceleration time. In tepid starts during regular driving, the transmission can feel slow to engage at throttle tip-in, but Vetter says this is because of the very conservative baseline of the car's adaptive shift programming. It will engage the clutches more aggressively over time if that is what it learns the driver wants, he said.

The company's aim was to avoid the jerky, abrupt engagement that can turn off first-time DCT drivers who are accustomed to the creamy smoothness of a torque-converter automatic transmission, Vetter explained.

The CLA45 has unique chassis details too. The GLA's engine sits nearly 2 in (50 mm) higher than that in the CLA-Class, providing for additional ground clearance. That clearance is 8 in (203 mm) in the GLA250, but only 4.8 in (122 mm) in the GLA45 as a result of its 2-in (50-mm) lower ride height than the GLA250 and because of its front air dam and other aerodynamic parts.

The GLA45 can even be equipped with front dive planes like those commonly seen on endurance racing sports cars and a rear spoiler atop its hatch that appears aimed at attracting buyers graduating from the Subaru WRX.

The GLA45 has stiffer spring and shock rates than the GLA250, but they aren't as stiff as those on the CLA45 because that car's buyers reported that its suspension may be too stiff for their liking, according to Vetter. "This car is more enjoyable to drive because it isn't so stiff," he said. However, the available Performance Pack is 20% stiffer than the regular CLA45 setup.

The GLA45's brakes are four-piston fixed calipers from Brembo in the front, squeezing larger 13.8-in (351-mm) rotors, compared to 12.6-in (320-mm) rotors on the GLA250. At the rear, the GLA45 uses floating single-piston TRW calipers with 13-in (330-mm) rotors in place of the 11.6-in (295-mm) units on the GLA250.

With the AMG Driver's package, these calipers are splashed with the ever-popular red paint and are more visible thanks to the larger openings in the 20-in wheels that replace the standard 19-in wheels.

The GLA45's top speed is electronically limited to 155 mph (250 km/h), but thanks in part to a slightly taller 4.13:1 final drive (compared to 4.60:1 for the GLA250), it is only 2 mpg thirstier in the EPA's combined rating, with an expected city score of 23 mpg and highway rating of 29 mpg.