The Infiniti Q50 made a pretty good impression when it replaced the G series for the 2014 model year. With its wide stance, aggressive lines, and eyebrow LEDs above the headlights, it said "I'm here" with authority. But the old VQ 3.7-l V-6 that produced 328 hp and 267 lb-ft—good for a 0-60 time of 5.2 seconds—was a little long in the tooth and didn't get great mileage.

With the Q50 up and rolling as the brand's top seller, Infiniti wants to widen its appeal. Gone is the VQ. A new four-cylinder turbo codeveloped with Daimler will represent the bottom of the range. But the real intrigue comes from the new VR-series 3.0-liter, V-6 twin turbo powerplant tuned for either 300 hp and 295 lb-ft or 400 hp and 350 lb-ft.

We were able to try the 400-hp version on urban and rural roads in and around San Antonio, Texas, and on a closed course designed to showcase its performance. The 400-hp engine is exclusively placed in the Q50 Red Sport 400, which is available in RWD and AWD versions, and, incidentally, in colors other than red.

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The VR itself is a pretty marked departure for Infiniti.

The aluminum block and heads result in an engine 40 pounds lighter than the outgoing V-6.

It credits both direct-injection and electric valve timing for better acceleration and lower emissions.

It adds a water-to-air intercooler.

The exhaust manifold is integrated into the head for weight savings and to shorten the flow path, reducing lag.

400-hp versions have a special sensor that, due to the high boost pressure (14.7 psi versus 8.7 psi in the 300-hp version), senses when the turbo is nearing its redline (220,000+ rpm).

All that, plus a few new features we'll get to, translates to a significantly more potent-feeling Q50.

When you hammer the gas from a stop, the Red Sport 400 immediately exhibits its throttle response. Next you'll notice the Dynamic Digital Suspension, which has two settings: Standard and Sport. The settings alter the valve-controlled dampers to make cornering flatter and feel a little firmer overall. But even set on Standard, the Red Sport 400 and its staggered setup of the Dunlop SP Sport Maxx Summer tires (245/40R19 front and big ol' 265/35R19

rubber at the rear) is no handling slouch, instead inspiring confidence in normal to fast twisty-road driving.

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As in the original Q50, this model is available with the Direct Adaptive Steering that garnered so much negative attention; the steer-by-wire system links the steering wheel to motors at the front wheel electronically.

Infiniti has been at work, though, making the system … work. The system is adjustable in a matrix of three modes (Sport+, Sport, and Standard) and three response settings (Dynamic+, Dynamic, and Default).

On its highest performance settings, the ratio and feedback could be called a bit twitchy. Just tooling around on legal roads, the Standard/Default setting provided the most natural feel—and importantly, it feels pretty natural. Better even than the electric power steering on non-DAS-equipped cars.

But on an autocross course set up by Infiniti, the Sport+/Dynamic+ setting turned the Q50 Red Sport 400 into a roaring, responsive funmobile.

See all 49 photos

See all 49 photos

The only bone we'd continue to pick is that Infiniti still says a DAS "benefit" is that it "filters out unwanted steering vibrations." Maybe for luxury buyers that's a benefit, but those wanting more of a sport sedan than a luxury vehicle would say very few of those vibrations are unwanted. Infiniti is also quick to point out that DAS is an important step toward autonomous driving.

And speaking of Sport+ mode, that brings us to the greatest addition to the Q50 outside the VR. Drivers used to have four drive modes to select from using a switch on the center console: Snow, Eco (which crudely and ridiculously pushes back against your foot during acceleration), Standard, and Sport. Now a Sport+ mode not only optimizes throttle response, steering, and suspension settings but also loosens up the stability control, which normally has a tendency to intervene early. Not in Sport+. The drivers in our group were able to get the Red Sport to rotate a bit, even at the relatively slow speeds of the test course. Being able to have some fun without turning VDC all the way off is a huge improvement.

See all 49 photos

See all 49 photos

The Q50 Red Sport 400 is available with Infiniti's new forward emergency braking tech, which joins this list of driver-assistance tech: lane departure warning/prevention, blind-spot warning/intervention, back collision intervention, and Infiniti's supremely useful Around View Monitor with moving object detection.

The lowest point of the Red Sport 400 may be its distinct lack of a powerful exhaust note. That shortcoming might be what enthusiasts decry most on the VR. Even on the initial Q50, Infiniti had so muted the sound that once was a hallmark of the G series that after numerous comments from press and owners, it released a bolt-on sport exhaust kit to augment the sound. Well, if you're asking bystanders to guess the power of the VR 400, they're likely to guess low. It's a near-silent exhaust with no rumble or gurgle whatsoever.

I asked an Infiniti engineer whether that was because they want it biased to luxury, and the response was something akin to, "Well, that can always change later."

The automaker isn't ready to announce pricing yet for the 2016 Q50 lineup, though it did say that the four-cylinder turbo will come in below the current $37,500 base price. Infiniti hinted that the Red Sport 400 will start at significantly less than $60,000, which is roughly the current going rate for most of the 400-hp luxury sedans in the market.