From a 2009 review...
The SLK 350 carries what Mercedes says is a 3.5-liter V-6 engine that has undergone a major overhaul and now produces 300 hp (32 more than the previous version) and 265 lb.-ft. of torque.
However, Mercedes says the high-revving engine also provides better fuel economy and thus reduced CO2 emissions. It is linked to the 7G-tronic automatic transmission, which blips the throttle during downshifts for enhanced sound, performance and durability. Mercedes promises that the engine “strikes a far more emotive-sounding note.” Changes to the 3.5-liter engine include a higher rev limit, increased compression ratio, new intake manifold and what Mercedes calls “extensive” modifications to the valvetrain.
Additional history:
The 3.5-liter version of the 280SE
was first introduced in 1970. It was similar to the base 280SE, but given a
performanceboost thanks to the potent power-plant. It was hailed by the company as a smooth and powerful engine. Zero to sixty was accomplished in less than ten seconds.
Additionally for diesel owners:
Mercedes-Benz USA now approves the use of B5 bio diesel (standard diesel with a maximum 5% bio diesel content) in all Common Rail Injection Diesel "CDI-engines." As bio-diesel can be refined from a variety of raw materials resulting in widely varying properties, the only approved bio diesel content is one that meets ASTM D6751 specification and that has additionally the necessary oxidation stability (min. 6H, proved with EN14112 method) to prevent damages to the system from deposits and/or corrosion. Please ask your service station for further information. If the B5 bio diesel blend is not sufficiently labeled to clearly indicate that it meets the above standards, please do not use it. The Mercedes-Benz limited warranty does not cover damage caused by the use of fuels not meeting Mercedes-Benz approved fuel standards.
