When a company with the engineering reputation of Mercedes-Benz embarks on a totally new engine program, everyone takes notice.
First, the Germans stunned the business when it was learned the new engine program, a modular range consisting of a variety of 6-cyl. and 8-cyl. powerplants, would do away with the longstanding inline 6-cyl. engines - a design for which Mercedes had become nearly as famous as its chief rival- in favor of a vee cylinder arrangement. The V-6 design is a first for Mercedes.
To add further intrigue, Mercedes engineers specified a single overhead-cam (SOHC), three-valve-per-cylinder head design - a transgression from the now-prevalent norm of dual overhead cams (DOHC) and four valves per cylinder for most newly developed engines.
There is method to the madness, as you would expect. Mercedes says the 3-valve arrangement is good for as much as a 40% reduction in certain emissions, because the single exhaust valve presents much less valve surface area than a comparable 4-valve engine, that translates into considerably higher exhaust temperatures and thus better cold-start emissions. Engineers are quick to add that there's no performance loss because total exhaust valve surface area is not as critical as it is on the intake side.
Fitting only three valves means more room in the head, allowing a twin-sparkplug arrangement, another Mercedes first - and again, the design is said to have unique emissions-cutting and power-enhancing benefits.
The fly in the ointment is the fact that Mercedes also builds V-8s from this "modular" design, so the vee included angle for both the V-6s and V-8s must be the same. Mercedes chose the 90-degree vee that is optimum for V-8s - but not so good for a V-6. So the V-6s are fitted with a single balance shaft, rotating counter to the crankshaft at twice its speed, to quell the primary-order vibrations inherent to a V-6 with 90 degrees between its cylinder banks.
A compromise from a company so steeped in a reputation for cost-is-no-object engineering? That's what we've heard a few competing powertrain engineers grouse when discussing the new Mercedes powerplants, saying Mercedes engineers of the past would never have settled for such an arrangement. It seems nothing is entirely sacred in this era of brutal cost rationalization.
We think the carping of competitors is sour grapes. On the road, Mercedes' new V-6s work. The 215 hp that moves the new CLK is much more convincing than that of any number of higher-horsepower cars, while this same 3.2L V-6 does a pretty respectable job of moving the hefty new ML30 sport-ute, too. And subjectively, any difference in NVH between the new vees and their predecessor inline engines is nearly imperceptible.
There are wily design touches throughout these new engines, like the Flexible Service System that uses a sophisticated thermoconductivity sensor to monitor oil condition and tailor change intervals according to specific driving conditions, not predetermined mileage intervals.
This is a solid, technically significant new engine range. The only thing given up to the old inlines is the lovely, ripping snarl under a hard throttle, something a vee engine just can't replicate.