Muscle, MPG and Mom

Infiniti's new '11 M sedan presents a great mix of ridiculous power, astonishing fuel economy and parental-like controls sure to please, and perhaps perplex, buyers.

The M's new 5.6L V-8 cranks out a whopping 420 hp and 417 lb.-ft. (565 Nm) of torque. But thanks to direct injection and other fuel-sipping features, we were able to average an astonishing 28.2 mpg (8.3 L/100 km) on one test route through southern California.

While some may think it sacrilege for a sport sedan, Infiniti has introduced an Eco mode and optional Eco pedal on the new M. Much like mom would do, both Eco technologies remind drivers, “Geez, Louise, ease off the gas.”

Other technologies, many of which can be turned off, suggest drivers “Pay attention, for Pete's sake!” Distance-control assist slows the vehicle when cameras and sensors detect the M getting too close for comfort to another car.

The M also can steer and apply the brakes when a driver drifts out of his lane (lane-departure prevention) or tries to move into a lane occupied by another vehicle (blind-spot intervention).

The Infiniti M, on sale now in the U.S., offers Nissan's 3.7L V-6 from the current G lineup and the new 5.6L V-8 that replaces the 4.5L V-8 in the outgoing M45.

Both mills are mated to a 7-speed automatic transmission.

The new M37's 3.7L V-6 makes 330 hp and 270 lb.-ft. (366 Nm) of torque, up from 303 hp and 262 lb.-ft. (355 Nm) of torque for the outgoing M35's 3.5L V-6.

The M37, which should account for the vast majority of sales, has a different personality from its larger-mill brother. Although its exhaust note is buzzy, the car feels more ready-to-run than the M56, with quicker throttle and shift responses.

Noise, vibration and harshness issues detected with the 3.7L in the G is muted in the bigger M. Infiniti's Active Noise Control, which uses the M's sound system to cancel out unwanted engine racket, may play a role in that improvement.

A standard center-console dial allows drivers to choose between four modes: Sport, Standard, Eco and Snow, each with unique throttle and transmission settings.

Most people cannot use 420 hp, or 330 hp for that matter, in daily driving, so an Eco setting that prioritizes fuel economy in large vehicles makes sense.

The RWD M56 is better for comfort cruises, with a deeper, less noticeable exhaust note. While it presents a more aggressive throttle tip-in than the '10 M45, which doesn't let loose until half-open throttle, the calibration feels timid compared with the M37 or Hyundai Genesis.

In aggressive driving over hilly terrain in the M56, with speeds between 30 and 50 mph (48-80 km/h), we average 20.6 mpg (11.4 L/100 km) in Sport mode. In Eco mode and with Eco pedal, the M56's fuel economy jumps to 28.2 mpg (8.3 L/100 km) with non-aggressive driving at similar speeds.

That is better than the 26.8 mpg (8.8 L/100 km) returned in an M37, in Eco mode and with Eco pedal on the same route, at the same speeds.

Eco pedal causes the throttle to resist even moderate acceleration demands, pushing back on a driver's foot. The sensation is annoying, and the pedal resistance extreme, when trying to travel uphill. But 28.2 mpg in the M is worth it.

All Ms continue to boast a double-wishbone front and multi-link independent rear suspensions. However, rear-suspension geometry is changed and laser welds are added to the mounting points to boost stiffness and provide a quieter, more composed ride.

Also reining in the rear of the M is Infiniti's 4-wheel Active Steer (4WAS) system, which turns the rear wheels in phase with the front wheels up to 1 degree to keep the car planted.

The new M is upgraded inside, with Infiniti disguising the few regrettable touches of hard-plastic trim (steering column) that remain by giving the material a nice gloss and texture. Aluminum and leather trims are of superior quality, as is a velvety fabric headliner.

Silver-like particles on the upgrade ash-wood trim lend a cool effect, but the high-gloss finish gives it a dated appearance.

The curvaceous lines of the exterior are repeated inside the car to great effect, most notably on the doors. Ergonomically, the M is an easy car to love. The protruding center stack puts all buttons within reach, even the sound system tuning knob, essential for skimming through voluminous satellite radio stations.

Roominess abounds both front and rear, but seating comfort is middle of the pack. Longer drives called unwanted attention to cushion firmness.

The M offers four well-appointed grades: M37 RWD; M37x (all-wheel drive); M56 RWD and M56x, all with standard leather seating and 10-way power driver and front-passenger seats.

The '11 M is an impressive automobile, thanks to its power, fuel efficiency and safety technologies. U.S. government statistics show nearly 6,000 people were killed and more than 500,000 injured as a result of distracted drivers in 2008.

With that in mind, a car that can steer itself out of harm's way certainly qualifies for Mom's seal of approval.

[+] PROS/CONS [-]

'11 Infiniti M56

Vehicle type: Front-engine, rear-wheel-drive, 5-passenger sedan

Engine: 5.6L DOHC all-aluminum DI V-8

Power (SAE net): 420 hp @ 6,000 rpm

Torque: 417 lb.-ft. (565 Nm) @ 4,400rpm

Transmission: 7-speed automatic

Wheelbase: 114.2 ins. (290 cm)

Overall length: 194.7 ins. (494 cm)

Overall width: 72.6 ins. (184 cm)

Overall height: 59.1 ins. (150 cm)

Curb weight: 4,028 lbs./1,827 kg

Base price: $57,550 ($46,250-$60,050 range for all Ms)

Fuel economy: 16/25 mpg (14.7-9.4 L/100 km)

Competition: BMW 5-Series, Audi A6, Mercedes-Benz E-Class, Lexus GS, Cadillac STS