Infiniti's mid-size sedan, the M, has been around for quite some time, but it's still one of our favorite luxury sport sedans. We lived with an M45 for a full year, and not once did it require repairs. Even those in the office who didn't initially understand the M45's place in the automotive world came away from the test in awe of how good this Japanese BMW-fighter really is.
For 2009, the M is available in four trim levels, as detailed below.
The M35 is the entry-level M, and it comes with a V-6 engine and rear-wheel drive. Last year's 275-hp VQ35 V-6 engine has been replaced with the HR (high-revving) version of the VQ. Displacing the same 3.5 liters, the VQ35HR produces 303 hp and 262 lb-ft of torque. It's mated to a seven-speed automatic transmission (up from last year's five-speed), so the M35 now feels as fast as its V-8-powered big brother. In fact, it only produces 22 less hp, and with the benefits of two additional gears in its transmission, it might even be quicker than the M45. The additional power comes at no extra fuel cost; in fact, thanks to the extra gears in the transmission, EPA fuel economy improves from 16/23 to 17/25.
The four-wheel-drive M35x receives the same engine upgrades as the base M35 but soldiers on with a five-speed automatic. However, like all 2009 M models, the transmission receives a new "DS" sport mode. DS is similar to the "sport" mode offered by many of Infiniti's competitors; it chooses a more aggressive gear selection map to keep revs up and maximize response. The upgraded VQ revs to a lofty 7500 rpm, but like most other Nissan V-6s, it's a little coarse in the upper rev range - use the DS mode at your own aural discretion.
Now that the M35's V-6 makes only a few fewer ponies than the V-8-powered M45, you might think that the eight-cylinder M is obsolete. Not so much - this is the Infiniti I would buy. The M45's 4.5-liter V-8 makes 74 lb-ft of additional torque, for a total of 336 lb-ft compared with the M35's 262 lb-ft. Much, much more important: whereas the V-6 is buzzy and coarse at high rpm, the V-8 is one of the best-sounding, smoothest V-8s on the planet. It creates such an orchestral noise that I routinely seek out tunnels when I'm driving an M45 - the marginal drop in fuel economy (to an admittedly thirsty) 16-mpg city, 21-mpg highway is well worth the soundtrack in my book. Furthermore, the V-8's prodigious mid-range torque practically begs you to power-slide the M45 around the neighborhood. With great steering and magnificent chassis balance to boot, the M45 is really hard to beat. Once Infiniti finally replaces the ancient (but super-smooth) five-speed automatic with its seven-speed unit, it might not be possible to beat the V-8-powered M at all.