SLK 55 AMG
0-62 mph (100 km/h) quoted at 4.9 seconds (Car & Driver Magazine reported 0-60 mph in 4.3 seconds.)
Increased brake capacity. 345x30mm brake discs (Pre-2008-model-year cars have 6-piston front calipers with perforated and slotted rotors, and 4-piston rear calipers. Later models have a mix of brakes depending on options and market: either the original 6-piston fronts or the 4-piston fronts from the C55. Mercedes made this change not only to cut costs but also to reduce complaints about brake squeal from customers not used to high performance brakes.)
Additional engine oil cooler (behind right-hand bumper vents)
Lowered/stiffened suspension (springs, shocks, sway bars)
18-inch alloy wheels with 225/40 front and 245/35 rear tyres.
AMG body kit, with distinctive gills in front bumpers
Chrome-accented fog lights
Napa leather interior
Quad exhaust
Smoked taillights and CHMSL
2008 facelift included a controller upgrade to the AMG SPEEDSHIFT 7G-TRONIC transmission, shifts 10% faster than previous model.

The second generation Mercedes-Benz SLK, internally designated model R171, is a two-passenger, front-engine, rear-drive, retractable hardtop roadster, unveiled at the 74th Geneva International Motor Show—and manufactured and marketed for model years 2004–2010. Currently in its third generation and manufactured at Mercedes' Bremen plant, the SLK nameplate designates Sportlich (sporty), Leicht (light), and Kurz (compact).

The R171 features a number of revisions compared to its predecessor, the R170: a 30mm longer wheelbase, increased length (72mm) and width (65mm), 40% increased use of high strength steel, seven-speed automatic transmission, adaptive two-stage airbags, head/thorax sidebags and a revised roof mechanism (marketed as the Vario roof) deployable in 22 seconds (previously 25 seconds) with a rotary-pivoting rear window enabling a more compact folded roof stack and trunk storage increased by 63 litres with the roof retracted.[6] Optional features include remote operation of the retractable hardtop as well as an innovative forced air, neck-level heating system integral to the headrests, marketed as Airscarf.

The fully galvanized bodywork, which features 19 percent improvement in static bending and 46 percent improvement in torsional strength with the roof down, also features a 3% improvement in aerodynamic efficiency, with a Cd value of 0.32. The design has been aerodynamically optimized to minimize interior draughts with the top retracted and includes a fabric windblocker which can be pulled up over the two roll-over bars. Mercedes marketed the R171's tapering front end styling by designer Steve Mattin as "Formula One-inspired".

In 2008, the SLK reached sales of 500,000. The R171 made Car and Driver's Ten Best list for 2005 and won the Canadian Car of the Year Best New Convertible award.

The R171 SLK were the last series that a manual transmission was available in a 6 Cylinder Mercedes-Benz Convertible. The successor to the R171, R172, only offered manual transmission in their 4-cylinder vehicles.

Car and Driver reviewed the manual transmission in November 2004 and rated the transmission glowingly as "..the love child of a Honda S2000 and BMW M3...". The review further wrote that with the SLK350 the engine "...has a willing personality that is perfectly suited to a manual transmission-you'll definitely not regret choosing it over the automatic.