2005 Mercedes-Benz CL65 AMG: Dyno Tested
March 25, 2014
Our long-term 2005 Mercedes-Benz CL65 AMG is defined by its numbers in a way that few cars are. Big weight, big dollars, big torque, big power. Even twelve cylinders weren't enough when Affalterbach was devising its looney-tunes M275 engine. It had to be a twin-turbo V12. With twenty-four spark plugs, because it needed another big number.
So we recently hit the dyno rollers in our CL65 AMG in pursuit of knowledge. First, of course, big numbers. But we also wanted to find out if age and miles have eroded this thing's ability to belt out the goods. Our performance testing of the big coupe was certainly an informative exercise to help flesh out the answer, but a dyno test can tell us so much more.
So, yeah: 6.0 liters, 604 horsepower and 738 lb-ft of torque when new. We headed to our usual dyno haunt, MD Automotive in Westminster, CA, and got busy with the CL65 AMG.
Here's what we measured at the wheels:
Well, then. Yes, that's 674 lb-ft of torque and 528 horsepower to the wheels. Factoring in driveline loss, it's safe to say this thing is still plenty perky despite its near-double digit age and almost sixty thousand miles on the clock.
What's more, the CL65 was freakishly consistent. Each pull was almost exactly the same to the horsepower as the prior one: just a smooth arc of torque accompanied by a muted whoosh. Easy peasy. It's the most relaxed, unstressed-feeling 600-horsepower engine on the planet...until the rev limiter cuts in. The CL65 AMG's brutally hard fuel cut was the most violent thing I've ever experienced in any car on the dyno. No soft rev limit here: the power slams off so hard at 5,200 rpm the entire car jerks the straps holding it down.
The engine revs low, like an old-school big-block pushrod engine. But, no, this is an SOHC mill, albeit still with only two valves per cylinder. I'd wager that the stock turbos are backpressuring the heck out of the engine at high revs, anyway, making more revs moot. Still, what a torque monster. It's too bad it's backed by such a mushy, syrupy automatic gearbox that saps out any snappiness this engine might have.
Automatic gearbox-equipped cars are always more tricky on the dyno than manual ones. Slushboxes think they're smarter than you, downshifting at inopportune moments (which results in an aborted dyno run). But the CL65 AMG turned out to be no problem at all. Just click it into manual mode and it will hold exactly the gear you choose. Imagine that!
By the way, the results you see above were achieved in third gear. I tried using fourth but there was a speed governor that shut the party before the revs ran out. So I went back to using third so that I could get a full pull all the way to the rev limiter. I'd expect even larger dyno numbers in fourth gear.
For kicks, here's how the CL65 AMG stacks up against the modern twin-turbo 5.5-liter M157 V8 in the 2012 CLS63 AMG. I dyno-tested this car on this same dyno a while back.
As equipped with the AMG Performance Pack, this car is rated at 550 horsepower and 590 lb-ft of torque at the flywheel. Er, flexplate. Or whatever.
In our testing the CLS63 AMG put down 514 horsepower and 543 lb-ft of torque to the wheels, placing it quite close to the power we measured at the CL65 AMG's wheels, while the torque delta as measured between the two cars is about what one would expect. Note the completely different character in the comparison above. The CLS63 AMG is quite the revver by comparison. The closer ratios of its 7-speed gearbox will also do a better job of keeping the modern car in the heart of its power delivery, too.
Nowadays, AMG backs the twin-turbo V12 in its *65 cars with a 7-speed gearbox instead of the 5-speeder in our CL65 AMG. Two more gears makes for bigger numbers in more ways than one.
Jason Kavanagh, Engineering Editor @ 59,580 miles