Mercedes-Benz 3.2L SOHC V-6

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 BMW -- 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-spark-plug 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 the crankshaft at twice its speed, 
to quell the primary-order vibrations inherent in 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 ppwerplants, 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 the engines 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 through out 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.


MERCEDES-BENZ 3.2L SOHC V-6


Engine type:  3.2L SOHC 90[degrees] 

V-6 Displacement (cc):  3,199 

Block/head material:  aluminum/aluminum 

Bore x Stroke:  89.9 mm x 84 mm

Horsepower (SAE net):  215 @ 5,500 rpm 

Torque:  229 ft.-lbs. (310 Nm) @ 3000-4,600 rpm

Specific output:  67 hp/L 

Compression ratio:  10:1 

Application tested:  CLK 320


Wards Automotive 10 Best Engines Award  January 1998