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Infiniti's new VC-T changes the rules of small turbocharged engines

The upcoming Infiniti QX50 crossover does not get our pulse racing, no matter how shapely the QX Sport Inspiration concept that previews it may be. No midsize SUV does, to be fair. But it has something special under the hood – the world's first production variable-compression-ratio engine. That means the QX50's 2.0-liter turbo four, which makes 268 horsepower and 288 pound-feet of torque, will have up to 27 percent better fuel economy. Here's how it works. The trend of moving to smaller, turbocharged engines carries with it one big falsehood. Under low load when the turbo isn't needed, these engines are less efficient than an equivalent engine without a turbo because of the low compression ratio the turbo requires. That is, if you never need the extra power, you're wasting fuel. Turbocharged (and supercharged) engines use a lower compression ratio to prevent detonation. When you force extra air in a cylinder and mix it with fuel, it's more likely to prematurely go boom. Lowering the compression ratio prevents this problem, but it's less efficient. Infiniti's VC-T promises the best of both worlds, with a compression ratio that ranges from 8.0:1 for high-power turbo needs to a 14.0:1 ratio for fuel-sipping efficiency. At its heart the VC-T engine is a simple idea, but it's complicated to explain. Consider yourself warned. The photo below from Infiniti serves as a good visual overview. For the truly nerdy, this patent application covers the mechanical concept. Instead of having the pistons connected to the crankshaft, Infiniti's engine has a pivot arm with a connection on each end. One end connects to the piston, the other connects to a second lower shaft, which is controlled by an actuator arm. At any given time the engine's pistons move up and down according to the lobes on the crankshaft. But the actuator arm can change the angle of the pivot arm up and down. That is, the pistons still move in the same motion with the same stroke, but phase the entire stroke up or down. Move the pivot up and there's less room at the top, which means a higher compression ratio. Move the pivot down and the compression ratio goes down, too. As an added bonus, the lower shaft eliminates the need for counter-rotating balance shafts. Infiniti says this system works constantly and can vary the compression ratio to any number between 8:1 and 14:1. It also uses electronic variable valve timing on the intake valves to switch into Atkinson-cycle combustion for greater efficiency.

2019 Infiniti QX50 First Drive Review | A high-tech engine flies under the radar

Update: An Infiniti representative reached out after this review was published and noted that the "Park with Easy Steering" function of the Direct Adaptive Steering system was erroneously left engaged. Infiniti says this feature "reduces feel considerably at low speeds to aid in parking", and that the Easy Steering function will be disabled by default in customer cars unless the customer chooses to engage it. This seems to explain the issues our reviewer had with low-speed steering feel, although we've had other problematic experiences with Direct Adaptive Steering in a broader sense – not to mention the fact that the drive-by-wire system has been recalled several times to fix various issues, and also recalibrated in response to criticism. We hope to get another QX50 soon, and if so we'll compare the low-speed steering response with Easy Steering on and off. Even as manufacturers rush headlong into electrification and autonomous driving, revolutionary internal-combustion engine technologies are still being developed. Consider the Mazda Skyactiv-X Spark Controlled Combustion Ignition process, for example. But Infiniti's VC-Turbo four-cylinder engine, which makes its debut in the 2019 QX50, is truly a work of engineering fortitude. The engine realizes the long-held ambition among engine manufacturers to create a way to alter the compression ratio on the fly, a boon to both power and fuel efficiency. It's a brilliant bit of science that's, unfortunately, still in search of the right car. Don't get us wrong, the QX50 is perfectly competent — it's an exceedingly quiet and comfortable cruiser. However, it's no longer the driver-pleasing machine its predecessor was. That car, originally known as the EX35, was built atop Nissan's sporty FM platform, a front-midship, rear-wheel-drive layout putting the engine aft of the front axle line and giving the vehicle the athletic driving dynamics of a sport sedan. In fact, it was basically a G37 hatchback, and it was sold as the Skyline Crossover in Japan. A shortened FM chassis underpinned the 370Z, to put a finer point on it. For those more concerned with comfort than corners, the 2019 QX50 might actually be a more useful. It rides atop an all-new front-wheel-drive chassis, which means it's able to add more space for both passengers and cargo. It trades a heap of the old QX50's sportiness for comfort and packaging efficiency. If that sounds good to you, perhaps the new QX50 is the right crossover.

Infiniti Q50 Red Sport 400 priced at $48,855, AWD at $50,855

Infiniti's most powerful production model, the new Q50 Red Sport 400, now has a starting price. You'll need at least $48,855 for the rear-drive model or $50,855 for all-wheel drive. (Both figures include the $905 destination charge.) A fully loaded, rear-drive Q50 RS400 with Direct Adaptive Steering, navigation, adaptive cruise control, a heated steering wheel, and Infiniti's entire alphabet soup of safety equipment, tops out at $57,045. (Again, add $2,000 for AWD). When it comes to rear-drive competition, the closest base price to the Q50 is the 320-hp BMW 340i. This German undercuts the Infiniti by two grand, $46,795 to $48,855. But the BMW outprices the Q50 as soon as you start selecting options. A 340i with similar equipment to a loaded Q50 Red Sport 400 costs just under $60,000. All-wheel-drive German competitors also lose out in the price war. Like with the rear-drive models, the BMW 340i xDrive undercuts the Q50 RS400 by around $2,000. Add the options, and the Infiniti becomes a better value. The other two big German rivals, the Audi S4 and Mercedes-Benz C450 AMG start at a higher price and only get more expensive. Technically the S4 starts cheaper than the Q50, but only with the standard manual transmission. Selecting the S-Tronic dual-clutch model kicks the price from $50,125 to $51,125, and going for the top-end Prestige trim will bump potential Audi owners up to $57,025. Throw on must-have S4 options, including adaptive cruise control, adaptive dampers, and a sport differential and you'll be shell out $64,425 for the Audi. The Mercedes-Benz C450 AMG is the priciest choice in this group, starting at $51,725, or roughly $900 more than a base Q50 RS400 with AWD. Options, again, are the downfall here. Building a C450 to match a loaded Infiniti will drive the Mercedes' price up to $64,315. While it occupies something of a weird space relative to these vehicles, it's also worth mentioning the Cadillac CTS VSport. It's the only car in this impromptu pricing comparo that can outgun the Q50, with its 3.6-liter, twin-turbo V6 good for 420 hp and 430 lb-ft of torque. It also starts at $60,950, although that includes plenty of standard equipment. All this means that the Q50 Red Sport 400 represents a relative value. It packs more power than the Germans – 80 more than the 340i, 67 more than the S4, and 38 more than the C450 – and a more comprehensive list of options, too.