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Published: 06/24/2013 - by Jason Kavanagh, Engineering Editor
In years past, the 2014 Mercedes-Benz CLA45 AMG would have been described as a sedan packing a hand grenade under the hood. Running unheard-of levels of boost in a turbocharged four-cylinder is a recipe for a wait-wait-kapow power delivery if one ever existed. Right?
Expectations, you have met your match. As AMG's entry-level offering in the U.S. market, the CLA45 AMG marks a new era for the in-house performance arm of Mercedes-Benz.
It's aimed at a broader and younger audience. Buyers who are less likely to have preconceived notions of four-cylinder power, and more likely to appreciate performance no matter how it gets delivered.
The project to transform the A-Class-based CLA250 sedan into something befitting the AMG badge wasn't always to be so ambitious. When work on the 2014 Mercedes-Benz CLA45 AMG began roughly four years ago, the original target for the direct-injected engine (eventually known as M133) was a "mere" 300 horsepower.
A short time later, senior brass moved the goalposts. They wanted 335 hp. The engineering team then undertook a feasibility study. Afterwards, the engineers reported that they wouldn't hit the 335 hp goal... because they were confident they could surpass it by an additional 20 hp. We imagine there was much rejoicing in Affalterbach that day.
Though the M133's fundamental architecture is shared with the base CLA250's engine, very few parts were carried over. It turns out that squeezing that much juice out of an engine that displaces a mere two liters entailed increasing peak cylinder pressures by more than 50 percent. As such, the block is now a stiffer sandcasting rather than a die casting, devised with a closed deck for better cylinder wall support and a rethought two-path coolant flow scheme.
The engine's entire bottom end — crankshaft, rods and pistons — is now forged, while the head casting has been revised with a new water jacket and fitted with lumpier cams and sodium-filled, nickel-based superalloy exhaust valves. Compression ratio dips to 8.6:1 to suit the 26.1 psi wallop delivered by an overhauled turbo system, now boasting a Schweinebraten-sized twin-scroll BorgWarner B03 turbocharger that feeds a short-path liquid-to-air intercooler.
A Benchmark Engine
The expected all-or-nothing, light-switchlike power delivery is nowhere to be found. This engine is astonishingly bright, tractable and transitions into boost with impressive linearity from as low as 2,000 rpm. It chews through revs with an effortlessness that masks its potency, thanks to a broad, tall swell of torque that forms a 332 pound-feet plateau between 2,250 and 5,000 rpm.
Mercedes claims it will run from zero to 60 mph in 4.5 seconds; we'd guess this estimate might even be conservative. Yet from behind the wheel, you'd never guess its engine boasts the highest specific output of any series-production engine. It's never anything but completely civilized, and it's stunning.
Considering the CLA45 is from a company so intimately associated with power-drenched V8 and V12 engines (one executive joked that they "used to use four-cylinder engines for the windshield wipers") the car's soundtrack will take some getting used to. It's unapologetically a four-cylinder sound. All the vocals come from the exhaust — there is no induction sound — and at full whack, the buzz from the tailpipe is prominent, if not exactly musical.
The barnstorming mill is offered solely with a seven-speed dual-clutch transmission and all-wheel drive. Its three operating modes, Comfort, Sport and Manual do a good job of covering the bases, though this isn't the quickest-shifting DCT in the land. And despite its seven speeds, there are large ratio drops when shifting into 3rd and 4th gear. At least each full-throttle gearchange is punctuated by a delicious, deliberate fwa-crack! from the exhaust.
Capable, if Flavorless Chassis
Most of the time, the 3,494-pound 2014 Mercedes-Benz CLA45 is driven by its front wheels. Only when the chassis and powertrain sensors deem it appropriate does the Haldex clutch pack located in the rear differential send power to the rear. Up to half of the engine's torque can be sent rearward in this manner. In practice the system works seamlessly.
Bilster Berg Drive Resort is a spanking-new private road course in central Germany, the 19 turns of which were defined by keen assessment of the natural terrain. Hot-lapping the CLA45 here confirmed impressions formed earlier while booting it down the local back roads: AMG's baby is a competent, if slightly one-dimensional, handler.
This is a capable chassis that's easy to drive fast. Within a scant few turns you're probing the progressive breakaway characteristics of its 235/35 Dunlop Sport Maxx RT summer tires, as the CLA45's handling is sure-footed and inspires confidence. The CLA45 isn't, however, an apex-assassinating rally replica, like some kind of German Mitsubishi Lancer Evo IX. Its handling is consistently nose-led, and the rear end resists attempts to upset its purchase of the tarmac.
At the same time, the taut, well-snubbed chassis exhibits no bad manners and plays nicely with its overachieving engine. Every element in the CLA's suspension was firmed up in its transformation to AMG status, yet it still manages to round the sharp edges off rough roads. Its electric steering is well-weighted and is capped off by a synthetic suede-wrapped steering wheel lifted from the E63. Torque steer? There is none. And despite our attempts to point the nose toward each apex by trailing the left pedal, the big brakes shrugged off each barrage of three consecutive hot laps with only a hint of fade by the end.
Looking for the Devil Inside
As befitting its price, the rest of the cabin is well-trimmed and stylish, with supportive, comfortable if firmly padded optional seats. The car's compact dimensions are evident primarily in the backseat only, as the trunk is deep and front passengers have plenty of space. EPA fuel economy has not been released. We project 28 mpg combined.
It's just another reminder that the 2014 Mercedes-Benz CLA45 AMG throws away the rulebook of four-cylinder performance. Its nearly $48 grand base price is substantial, however, and the traditional gleam-in-eye AMG character has been toned down in favor of all-round appeal. Its level of success will be a litmus test of younger buyers' perceptions.
For sure, we won't look at four-cylinder engines the same way ever again.
Edmunds attended a manufacturer-sponsored event, to which selected members of the press were invited, to facilitate this report.