The M45x's fuel economy ratings - 14 city, 20 highway - are the same as those of the FX50, Infiniti's large SUV that not only outweighs the M45x by over a thousand pounds but also produces significantly more horsepower and torque (390 hp, 369 lb-ft of torque) from a bigger engine (5.0 liters instead of 4.5). There are two reasons for that. First, the FX's 5.0-liter V-8 uses VVEL, Infiniti's take on BMW's Valvetronic, a system that continually and infinitely varies valve lift - instead of using a throttle plate - to regulate power. And, second, the FX50 uses Infiniti's seven-speed transmission, which has a much taller top-gear ratio. The reason these technologies haven't trickled down to the M is simple: the M is nearing the end of its life cycle, and the FX is brand new. That means you can be sure the next-generation M will have more gears in its transmission, and it'll likely boast a serious improvement in fuel economy - its current Achilles heel. If you can get past the fuel economy (and one full-throttle run listening to that V-8 scream should do the trick), the M45x is the perfect foul-weather alternative to the rear-wheel-drive M45. Which is a very compelling alternative to (and in some ways a better car than) the BMW 5-series. Praise doesn't come much higher than that... and besides, you can't get a V-8-powered all-wheel-drive BMW 550i.
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