So we dyno-tested the 2011 Mercedes-Benz S63 AMG, the first AMG car that we've had in our care sporting the company's new 5.5-liter biturbo V8.
Yeah, uh, can you say "torque"?
There's a certain upside to the world's ever-increasing scrutiny of fuel consumption and CO2 emissions: turbos.
Mercedes-Benz' AMG division has relied on normal aspiration in recent years, its 6.2-liter V8 playing the role of workhorse for virtually every model in their range including the silly R63 and ML63 SUV things.
That engine is gradually being phased out in favor of a direct-injected, twin-turbo 5.5-liter V8 that stirs up 536 horsepower and 590 lb-ft of torque. Not only does the turbo engine -- called M157 -- belt out more grunt than the erstwhile aspro mill, it's also more fuel-efficient.
And if that's not enough for you, there's an optional AMG Performance Package that ups the boost to 15.6 psi for a stonking 563 horsepower and 664 lb-ft of torque. The Performance Package functionally is nothing more than different calibration that gets uploaded at the factory. It's a $7,300 option that's equipped on our S63 test car. So, yes, AMG knows how to make money.
It also knows how to make torque. To wit:
Holy slab-o'-torque! This thing just serves the stuff up as if it mistook the Stanley Cup for a ladle. Torque hovers around 600 lb-ft from 2600 to 4600 rpm before progressively ramping down to 426 lb-ft at the 6300-rpm fuel cut. This is no fluke run, either, as the car just kept making more and more power before stabilizing at this output. Power peaks at 537 horsepower at the wheels. Strong? You betcha.
Due to the dollop of boost, there's less of a need to rely on revs to make power, so the new engine checks out several hundred rpm sooner than the 6.2-liter engine. Some will miss the delicious sound of that engine, but this turbo engine is surprisingly vocal in its own right, with an unexpected basso profundo to its exhaust note.
The bare numbers don't convey just how much stronger the turbo engine is than the outgoing 6.2.
Here, this is how the S63 stacks up to the SLS we dyno-tested last year, which boasts the M159 engine, the highest-output version of the normally aspirated 6.2-liter V8. It's a straight-up ass-whooping.
Still miss the 6.2? Yeah, okay, I do too, in a way. It's a helluva engine.
Geeky tech note: Chassis dyno plots of turbo engines rarely match the shape of those published by automakers. In the latter case, you see these perfectly flat tabletop torque plateaus that appear drawn with a ruler, and the plateau usually starts at a lower engine speed than what you see on a chassis dyno plot.
One big reason for this is that the automakers use engine dynos. These load the engine much differently than do chassis dynos.
On an engine dyno the operator can load the engine at very low engine speeds for as long as he/she likes, which gives the turbos all the time necessary to reach the speed they "want" to reach for that condition. Engineers call this "quasi-steady" operation.
Inertia chassis dynos -- like the Dynojet 248 we use here -- don't have load-holding capability. The engine speed during a pull is continually changing in real time, and the turbos have to play catch-up to the accelerating engine. And the shorter the gear, the more pronounced this catch-up effect.
To demonstrate this effect I performed a single pull in fifth gear after doing all of the other runs in fourth.
Again, when in a higher gear, the load on the engine is prolonged, and so the turbos spool up sooner (with respect to engine speed), resulting in more torque at lower engine speed. This is expected, and this is why you see the torque crossing 600 lb-ft about 400 rpm sooner in fifth gear (blue) than in fourth (red).
The jump in peak torque to 644 lb-ft in fifth gear -- up from 611 lb-ft in fourth -- is more of a surprise. A welcome one, I'd say.