2012 Mercedes-Benz CLS63 AMG Dyno Tested

You've probably heard that the 2012 Mercedes-Benz CLS63 AMG no longer carries its namesake 6.2-liter "M156" V8 engine. And that in its place is some puny 5.5-liter thing. 

Two words: twin turbo. It's a twin-turbo 5.5-liter thing, complete with liquid-air intercoolers and direct injection. The 2012 CLS63's power plant is called the M157, making it one better than the normally aspirated M156. 

After the M157-havin' CLS63 AMG clicked off an eye-opening  121.3 mph trap speed nbsp;at the test track, we figured it was high time for a trip to MD Automotive's chassis dyno.

In years past, the ability for an automaker to offer, say, two distinct horsepower levels in a car entailed major engine hardware changes -- increased displacement, more cylinders, revised valvetrain, higher compression pistons, the list goes on. This adds cost and complexity, which in turns adds more cost. Automakers loathe complexity.

By contrast, a bread-and-butter turbocharged engine can slam out heaps more power or torque (or both) with little more than a software change. This, as the kids say, is relevant to their interests.

Example: those for whom the standard CLS63 AMG's rated output of 518 horsepower and 516 lb-ft of torque is just too feeble have an option. Literally, they have the option of shelling out an additional $7,300 for the AMG Performance Package option which -- among other things -- brings the CLS63 AMG's tally to a more reasonable 550 horsepower and 590 lb-ft of torque. And not a single nut or bolt under the hood is turned in order to achieve it.

Naturally, our CLS63 AMG tester was equipped with the AMG Performance Package. Here's what it put to the ground:

Well, there's your trap speed. That's 514 horsepower and 543 lb-ft of torque to the wheels. Very resistant to heat soak, too -- run after run, power kept creeping up. After ten pulls it still hadn't nosed over, but it had finally stabilized to the values you see above.

And what a sound. Many turbocharged engines' character is soaked up and squirreled away by the turbos. Not the M157. AMG has retained a surprising amount of the M156's aural character in the M157. Good show, boys.

If two distinct power levels is good, four is better. Last year we dyno-tested a 2011 S63 AMG. It, too, is equipped with said 5.5-liter turbocharged V8. And it, too, is offered in yet two more levels of potency.

It's enough to make you question whether there's any truth behind all of this horsepower number parsing. 

Doubt no more:

AMG's strategy of liberating horsepower with nothing more than a few lines of code may be sneaky, but the differences are real. 

Bonus edition - after all of the CLS63's fourth-gear dyno runs were completed, I did a sole pull in fifth gear. Normally I stay away from such tall gears on the dyno for a number of reasons, but I wanted to double check what I'd found during my time with the S63. And just as with the S63, the CLS63's fifth gear run showed that the low end picked up and the midrange fattened. 

It's the "quasi-steady" influence at work -- in higher gears, an engine dwells at any given RPM for a longer period of time, more thoroughly pummeling the turbochargers' turbine wheels with exhaust pulses and allowing the turbo speed to more easily "catch up" to the increasing engine speed. 

This, in turn, brings the boost up at a lower RPM in the rev range, resulting in the improved torque you see around 2000 rpm. The fatter midrange? Not as straightforward since the wastegates are fully in play at this point. It's possible that the ECU allows a slightly higher boost target in higher gears.

However you slice it, the M157 has big brass ones. Makes me wonder how it will stack up against some American iron. Let me think about that and get back to you.