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With a 340-horsepower V-8 engine driving the rear wheels, M45 is a fast machine with lots of appeal.

A new addition that fills out Infiniti’s middle range, it’s also a conservative-looking sedan that fails to register many second glances. And based on a long-running Nissan staple in Japan, M45 is saddled with some aging chassis technology.

Nissan and its luxury division, Infiniti, have been creating remarkable cars and trucks in the past few years, turning the Japanese automaker away from the brink and back on solid ground. Infiniti is being set up as a luxury/performance brand, leaving the cushy pure-luxury realm to archrival Lexus.

Although Infiniti’s redesigned Q45 flagship and new G35 are stylish and sporting, the M45 is something of a mixed bag. Engine power sparkles, but the overall driving experience is not as bright as it could be. And styling falls short of Infiniti’s other shining stars.

Engine and transmission:

The powerful 4.5-liter V-8 is the same engine that motivates Infiniti’s flagship, Q45. Only here, it’s in a lighter, more maneuverable vehicle.

Competitors have to get up into their premium-priced performance range, such as AMG for Mercedes, to match the engine power in the M45. Off-the-line acceleration is strong, so much so that a careless push of the throttle can rocket you into trouble before you know it. Under way, things settle down a bit, though this V-8 is always ready to pull.

Smooth and quiet, the engine provides a sophisticated aura for the M45, not just power. The 4.5-liter is the only engine available, along with a five-speed automatic with a manual-shifting mode.

Handling and drivability:

The M45 drives and handles nicely, but its road manners are not nearly as impressive as its engine power. What’s lacking is the solid ride and responsiveness of the European sports sedans, such as Audi’s S6, or Infiniti’s smaller G35.

Based on the chassis of a Japanese home-market product, the Nissan Gloria (which is widely used as a taxi), the M45 seems dated despite all the power, electronic equipment and luxury features.

The speed-sensitive rack-and-pinion steering is quick and direct, and the suspension works to keep the M45 level in turns and steady on the road. But all together, not considering the engine power, the M45 feels bland and unremarkable.

Braking is good, via four-wheel vented discs enhanced with anti-lock; brake assist, which boosts brake pressure in panic stops; and electronic brake distribution.

Styling:

The midsize Infiniti is surprisingly plain looking, especially in relation to the edgy, forward-looking styles of such recent Nissan and Infiniti cars as Altima, Maxima and the G35. The M45 is attractive, with nicely creased character lines, a good-looking grille, projector headlamps and a purposeful appearance. But it fails to stand out like other recent Nissan and Infi niti products.

Interior:

The black-leather cabin looks businesslike, with supportive seats, bird’s-eye maple trim and Infiniti’s customary analog clock, which is handsome and jewel-like. The back seat is tight on legroom, and the center hump (remember, this is a rear-drive car) makes the center seat fairly useless.

The center video-display control panel, similar to that in the Q45, is a real pain. The audio and climate control share the digital array, which requires manipulating the screen every time you want to change a station or change the temperature setting. That’s an extra step and extra time with your eyes off the road to manipulate the controls.

The control knobs on the center binnacle are haphazardly and illogically arranged. Maybe you eventually get used to them, but in a weeklong road test, it never came easy.

The interior is enhanced with a load of standard luxury features. There’s a 225-watt audio system with seven Bose speakers, along with a six-disc CD changer that sounded really great. Also standard are dual-zone temperature control with rear-console ducts; leather seats and steering-wheel rim; and front and rear side-impact air curtains.

Optional technology includes a DVD video-display mapping system, a laser-guided cruise control that maintains following distances behind traffic, and the Voice Recognition System from the Q45. None of this stuff was on the test car.

Pricing:

The base price of $42,300 seems steep, with the Q45 starting at just a few thousand more. For that money, you do get that sparking engine power and a bunch of luxury and performance gear, but competition from BMW, Audi, Volvo, Mercedes-Benz, Cadillac and Lexus is pretty stiff in this range.

The test car included: a large sunroof, $1,000; a comfort and convenience package of tire-pressure monitor, full-size spare, Homelink transmitter, driver’s memory seat, anti-glare mirrors and an electronic compass, $950, which seems like a lot; a trunk mat, $60; and shipping, $545. The total is $44,855.

Bottom line:

A fast sedan with a load of luxury and performance features, the M45 fades in the face of heated competition, despite its horsepower advantage.

Infiniti M45

Vehicle type: Five-passenger, four-door sedan, rear-wheel drive.

Base price: $42,300.

Price as tested: $44,855.

Engine: 4.5-liter V-8, 340 horsepower at 6,400 rpm, 333 pound-feet of torque at 4,000 rpm.

Transmission: Five-speed automatic.

Wheelbase: 110.2 inches.

Curb weight: 3,851 pounds.

EPA mileage: 17 city, 23 highway.

Highs:

Engine power.

Luxury features.

Attractive interior.

Lows:

Mundane styling.

Uninspiring road feel.

Dashboard control woes.