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2013 Infiniti M56 review: Infiniti's 420-hp sedan is the opposite of efficient

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The Good The 2013 Infiniti M56 sedan packs a very potent level of standard infotainment features and audio sources. The Technology package adds a number of clever and forward-thinking driver aid features.

The Bad The 420-horsepower sedan simply isn't fun to drive. The Eco Pedal feature is awkward and didn't really help the V-8's efficiency very much.

The Bottom Line The 2013 Infiniti M56 is plenty powerful, but its true strengths are its safety and its cabin. Save your money and opt for the smaller engine.

Visit manufacturer site for details.

7.3 Overall
  • Cabin tech 8
  • Performance tech 6
  • Design 8

Review Sections

The Infiniti M37 sedan starts at $48,700, but our 2013 M56 sedan starts at a base price of $63,700. What do you get for the extra $12,500? About 1.9 extra liters of displacement that's about a Honda Civic's worth of engine size and power. That's an impressive little source of bragging rights there, but does it really make this flagship sedan better than its more modest sibling?

420 horsepower V-8
The 5.6-liter V-8 engine that spins its crank under the M56's hood outputs 420 peak horsepower and 417 pound-feet of torque. The engine is mated to a seven-speed automatic transmission, the only gearbox available on the M56, which sends power to the rear axle. Users have the option of upgrading to an all-wheel-drive system, but our vehicle was not so equipped. The transmission features a manual shift mode that is activated by moving the shifter to the left and rocking the lever back for rev-matched downshifts and up for upshifts.

On the center console, drivers will find the Drive Mode Selector knob, with which you can select one of four different driving modes. Sport puts the gearbox into its most aggressive mode, holding each gear longer for peak power and blip-downshifting when braking in preparation for a corner. Eco slightly detunes the output and throttle map and short-shifts each gear for smooth, economical driving. The Eco mode also activates an optional feature called the Eco Pedal, which we'll return to momentarily. Normal is, of course, the baseline performance mode, and Snow optimizes output for maximum traction in slippery conditions.

Our M56 was equipped with a $5,650 Sport package, which bumps the standard 18-inch wheels up to 20-inch, five-spoke rollers shod in stickier, performance tires. Nested in those wheels, you'll find four-piston sport brakes up front and two-pot stoppers on the rear axle along with upgraded sport suspension components with stiffer springs. The Sport package also adds a feature called 4-Wheel Active Steering.

The 4-Wheel Active Steering system adds a few degrees of steerability to the wheels on the rear axle, working automatically and in tandem with the front wheel's steering. At low speeds, the rear wheels' angle counters the direction of steering to reduce the turning radius and required steering-wheel effort. At high speeds and during lane changes, the rear wheels angle in the direction of steering to increase vehicle stability. At any speed, you probably won't notice that the seamlessly integrated system is actually doing anything.

Finally, the Sport package finishes up with magnesium paddle shifters for easier shifting, sport seats with deeper bolstering, and a number of styling upgrades inside and out to complete the "sport sedan" look.

On the road
If you're looking at the specs -- 420 horsepower, Sport package, 4-Wheel Steering -- and thinking that the M56 is a brute in a suit, think again. I found the M's performance to be largely understated, almost to a fault.

5.6-liter V-8
You pay a lot of extra dough for the M56's larger, V-8 engine. Antuan Goodwin/CNET

The engine doesn't impose itself on the driving experience, most of the raw power being smoothed out by the automatic transmission's smooth shifts -- even in the sportiest mode. The sport-tuned suspension is remarkably smooth and well-damped despite its big ol' wheels and the handling is well-composed and planted. If the 4-Wheel Active Steering system is doing anything, you wouldn't be able to tell from the driver's seat; it's that seamless in its operation.

However, the M56 just doesn't reward the sort of spirited driving that its bright red "S" badge would seem to encourage. The vehicle doesn't hide its size at all and doesn't seem to enjoy being hustled around a corner. Matt the go-pedal and your ears will be treated to a remarkably wheezy engine note -- this does not sound like a 5.6-liter V-8.

I'm not saying that the M56 can't handle itself at high speed, but I found myself having a hard time reconciling paying a base price of over $60,000 for a car that didn't feel more special than a G37 (ahem, Q50) sedan. At the end of the week, I realized that I'd not spent much time driving the M56 fast. With the M37 sedan offering the same level of luxury, I figure that if I'm going to drive slowly, I'd rather skip the V-8 and do it with an extra $12,500 in the bank.

The Eco Pedal
With its Drive mode selector in the Eco position, our Technology package-equipped M56 was able to take advantage of a feature called the Eco Pedal. This feature adds a small motor to the accelerator that can add resistance and movement to the pedal travel. Like most cars' efficiency modes, the M56's Eco mode is able to slightly detune the engine output, adjust the throttle map, and adjust the shift points of the automatic transmission to squeeze a few extra miles per gallon out of the power train. However, with the Eco Pedal active, the M56's computer is able to add resistance to travel to discourage lead-footedness. Give it too much gas and the Eco Pedal will even push back on your foot, recommending haptically that you take it easy.

This Eco Pedal's push-back is easy enough to simply press through for those moments when you genuinely need to get up and go, such as during highway merges or when making a passing maneuver. However, the feeling that the car simply doesn't want to do what you tell it to is unnerving. The driver can adjust the Eco Pedal between two levels of resistance (standard and a reduced setting) and totally defeat it using the touch-panel interface.

Drive selector knob
Place the Drive mode selector into Eco and the optional Eco Pedal will push back on your lead foot. Antuan Goodwin/CNET

I forced myself to stay in the Eco mode for about half of my driving in an attempt to fully test the system, but at the end of the week with the M56, I still found the slight hesitation that the Eco Pedal system can cause and the pedal push-back to be quite annoying. I can understand wanting to eke a few extra miles out of every gallon of fuel, but this technology seems a bit out of place on a 420-horsepower sport sedan with an EPA-estimated 19 mpg combined average. City and highway estimates are 16 and 24 mpg, respectively, but we were unable to crest 13 mpg, even with a heavy emphasis on highway driving for our testing. If you really care about fuel economy, the 5.6-liter variant is probably not the M sedan for you -- instead, take a look at the Infiniti M Hybrid.

Driver aid tech package
The $3,050 Technology package that adds the Eco Pedal also adds an array of other driver aid features.

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