Although Infiniti makes an upscale distinction from Nissan with vehicles like the G37 and FX35, its top-of-the-line M sedan never came up to the stately luxury of flagship sedans from BMW, Lexus, and Mercedes-Benz. For 2011, Infiniti updates its M56x to push power and interior quality substantially higher than what previous versions had, but it's still not at a level where we would suggest hiring a chauffeur.
In fact, with its Technology package, there seems little need for a driver at all. Not only does the M56x sound an alert if the driver lets the car drift across lane lines, it also has offside wheel braking, which is just a pulse, that helps to nudge the car back into its own lane. If the car detects the traffic ahead of it start to slow down, the M56x applies the brakes, bringing itself to a full stop. Just about the only thing the Infiniti won't do is time travel to 1984 and hunt down Sarah Connor.
Infiniti pioneered these groundbreaking driver assistance technologies, and the M56x benefits by getting the full suite. We have tested adaptive cruise control systems in different Infiniti models as well as cars from other automakers. With this feature active, we drove the M56x down the freeway, set the speed, and watched as it slowed down automatically when approaching traffic. One issue we noticed with Infiniti's system is that when a car cut in front of us, the radar would lose its lock, and the M56x would immediately lift up on the gas and slow dramatically until it regained a radar lock. We understand why Infiniti programmed it this way, but the driver behind us probably didn't.
Distance Control Assistance and its associated Intelligent Braking work like adaptive cruise control, hitting the brakes on the M56x for traffic stopped or slowing ahead. This system is a little more controversial, as it pushed back on the gas pedal when we approached stopped traffic, making us feel like we were fighting with the car. In dense city traffic, it was problematic, because it brakes and stops the M56x a full car length behind other cars, but in lighter suburban traffic that kind of stopping distance would be more acceptable.
Ultimately we learned to work with DCA, resisting the gas pedal push-back so we could tuck in closer to stopped traffic. This technology will prove useful for perpetually distracted drivers, preventing rear-end collisions. However, we also found that it seemed to get a lock on traffic ahead only about 50 percent of the time, so we couldn't always rely on it to stop the car. DCA feels like a tech novelty at this point, and is not turned on by default.
Active Eco mode
Another unique tech feature on the M56x, which also might prove to be controversial, is its Eco mode. Rather than merely dial down accelerator response and show economy performance on the dashboard, as other systems do, Infiniti's Eco mode adds resistance to the gas pedal, making it harder to push. We found we could push through the resistance to get a more satisfying start, but following the pedal's dictates made 0-to-25-mph runs take more than 10 seconds.
Infiniti instituted Eco mode in the M56x because the car's new V-8 is the biggest engine yet in an M sedan. This monster displaces 5.6-liters to generate 420 horsepower and 417 pound-feet of torque, putting the M56x on par with luxury competitors. Although Infiniti uses a technology it calls Direct Injection Gasoline to control the injectors, this car uses standard port injection, not the direct injection into the cylinders that other automakers are using.
At 16 mpg city and 23 mpg highway, the M56x's fuel economy isn't terrible considering its engine size, but it might be improved through true direct injection. We turned in a fuel economy of 17.6 mpg, with the car's seven-speed-automatic transmission proving crucial for raising the average during freeway travel.
Lacking a dedicated sport mode, the automatic transmission sets the tone for this luxury cruiser. It did just fine on the road, downshifting readily when we hit the gas, and keeping the engine speed low at freeway speeds. But no sport mode or paddle shifters for the manual suggest the M56x isn't designed for power cornering. The transmission's manual mode seems more suited for hill descents.
However, the same dial that turns on Eco mode also has a setting for Sport. This setting dials up the responsiveness of the gas pedal. Think of it as anti-Eco mode. In Sport mode, the car delivers very satisfactory acceleration. During fast starts, the M56x leaped forward willingly and proceeded with a fairly smooth acceleration curve.