In this generation, the M37 and M56 make more distinct cases for themselves. Base versions share an uprated version of the corporate 3.7-liter V-6, rated at 330 horsepower and 270 lb-ft of torque, for a 25-hp bump over the 2010 model. The V-6 version has the noticeable, vibration-ridden feel of a modern-day Nissan, and it needs to improve. At wide-open throttle the M37 is loud and transmits a lot of unwanted shake into the steering column and floorpan that’s sure to be noticed by any buyer in the $50,000 sedan segment.
Over the course of a day near San Diego, we spent far more time in the V-8-powered M56, for good reason. Only a few thousand more dollars replaces the V-6 with a hellacious 5.6-liter V-8 engine, the easy choice between the two 2011 M sedans. This version drills out 420 horsepower and 417 lb-ft of torque--almost 100 hp more than the last V-8 M—and thunders along with AMG-style power. Though the engine block’s related to the Titan pickup’s V-8, not the old 4.5-liter Infiniti engine, we noticed just a small vibration in one all-wheel-drive version; otherwise the M56 fleet we sampled ran startlingly fast, and built up speed with amazing force.
Both engines pair up with a seven-speed automatic transmission with a manual-shift mode, rev-matching, and available paddle shifters. The transmission likes to hold on to gears a long, long time, but downshifts snap off quickly, and the Ms are happy to pound out quick, unobtrusive gear changes at your command when the automatic’s moved to manual mode. We’re big fans of shift paddles, and the M56 shows exactly why shifter-based manual modes are goofy: who wants to remove a hand from the wheel while you’re diving into a 15-mph corner? Like the German competition, the Infiniti M automatic also adds an optional set of electronic controls for transmission shifting and throttle response, with four individual settings (Sport, Normal, Eco and Snow). You’ll be fine leaving it in Normal almost all of the time.
Great handling--quick, responsive steering and capable, supple ride--are an elusive mix, and Infiniti's nailed it. The steering has the right weight and turn-in feel. The rear-wheel-drive chassis is balanced and responsive for such a long car; all-wheel drive is an option, and doesn’t dull that edge too much. All versions ride over the worst surfaces with aplomb. The suspension remains a control-arm and multi-link design; a Sport package for rear-drive cars adds sport tuning for the suspension and sport-duty brakes, along with 20-inch wheels and four-wheel active steering, and it’s our preferred setup—not too hard, not soft at all. Available Active Tracing Control manipulates power levels and anti-lock brakes to help the M sedan corner more quickly. And big, strong brakes on all versions come standard with lots of pedal feel.
An M35 Hybrid is planned for the 2012 model year.