Renntech Slk 3.8I went to junior high with a guy named Ray. Ray had flunked a few years because of a learning disability, but even so seventh grade wasn't any easier for him the third time around. As expected, Ray excelled in gym class. Dodge ball was especially frightening when he was on the opposing side winding up for one of his highly accurate bean balls. He scored the most goals for the soccer team and was even known to win fights against high-school kids. While Ray was bragging about his sexual exploits, the other guys in school were still quietly confused about the changes occurring to their pre-pubescent bodies. People spoke about Ray in hushed tones, fearing that what they said might get back to him and awaken the Hulk within. It was out of respect.
Consider this RENNTech SLK 3.8 the automotive version of Ray, with more brains. Packing 291 bhp and 305 lb-ft of torque, it out-muscles and out-classes other SLKs, making the move up from sporty car to sports car, deserving to be mentioned in the same sentence with M3s, M Coupes, S4s and Boxsters.
The first thing you notice about this car is its wheels. Striking, multi-spokers called the Monolite by RENNTech because they're forged and weigh a scant 20 lb at 8.5x18 in., the rears are 9.5-in. wide. Second come the front brakes, monstrous, 14-in. cross-drilled discs squeezed by four-piston Brembos. A walk-around reveals dual exhaust tips stamped with "RENN" and "Tech" on each tip and low-key badges. Like other Mercedes tuners, RENNTech prefers to the keep things fairly subtle outside, concentrating on the innards.
With a turn of the key, you quickly realize that something sinister lives under the hood. The 2.5-in. stainless-steel exhaust system emits low-frequency burbles and warbles that can easily be mistaken for heavy Detroit iron. A blip of the throttle rocks the 3.8 on its mounts and the exhaust burble quickly becomes a scratchy growl.
To take it from 3.2 liters to 3.8, RENNTech bored out the cylinders to 97mm, up from 89.9mm. Stroke remains the same at 84mm. New camshafts made in Germany according to RENNTech's specifications reside in ported and polished heads. All moving parts were balanced and the engine also received a blueprinting. The stock airbox has been replaced with that from a 5.0 V8 engine, and the intake tubes are also larger in diameter. The ECU has been reprogrammed, including a 6400-rpm rev limiter and a top-speed limiter raised to 180 mph. RENNTech will easily admit that its 3.8 won't push the car to 180, however the 160 range is not out of the question.
With 305 lb-ft of torque available from 2500 to 4700 rpm, it's easy to loaf around in the higher gears. Passing doesn't require a drop down in gear either, but then you'd be missing the point. Going down from sixth to fourth at, say, 70 mph and nailing the throttle is this car's reason for being. The gravelly cackle of the exhaust and the way the torque presses you into the seatback might have you thinking there's a small V8 under the hood. And even though there's more torque than horsepower, the engine isn't reluctant to rev up to 5850 rpm and beyond just to extract the 291 bhp. The combination of a snarling V6 and a roaring exhaust make this SLK more menacing than any Mercedes has ever aspired to be.
Even more impressive than the acceleration is the deceleration. The 14-in. rotors in front and 12-in. rotors in back swipe off huge chunks of speed in an instant. Better than a $10-million insurance policy, they're soooo good they take getting used to and redefine the term late-braking.
Go hard into the corners after trailing the brakes and the short-wheelbased SLK darts quickly to the apex. Such agility makes it perfect for tight canyon switchbacks. RENNTech lowered the car 1.5 in. with shorter springs and Koni shocks valved to its specs. The ride is impressive, never harsh and seemingly more compliant than stock. Only a series of bumps and undulations will make the ride seem choppy. RENNTech wrapped its Monolite wheels with Pirelli P-Zero Rossos (235/40ZR-18 front, 265/35ZR-18 rear) that give plenty of audible warning when encroaching their limits, which also helps compensate for the steering's lack of information.
Rowing the box, however, isn't quite as satisfying. The six-speed shifter is unmodified and, as is, feels too light and flimsy, out of character for the rest of the car. It begs for a short shifter, with a heavier feel and more indication of engagement.
Some might argue that AMG's supercharged SLK will outrun this RENNTech 3.8, to which it's hard to argue. But that car won't be offered with a six-speed, and, if the owner of this car ever feels his car is lacking, Hartmut Feyhl, of RENNTech, says the AMG supercharger can be retrofitted to the 3.8. Then, as Mr. Feyhl, said, the 180-mph top-speed limiter might become relevant.
As for Ray, last I heard, he went to reform school upstate.