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Infiniti's variable compression engine in the 2019 QX50 is the first of its kind

The world's first variable compression ratio engine is here, in a production car. That car is the 2019 Infiniti QX50, debuting this week at the Los Angeles Auto Show. The midsize crossover has seen a refresh that has brought it an all-new platform together with new driver assist features, but it's the engine that's the centerpiece here. Nearly everything is continuously variable under the hood of the QX50 – not only the new shift-by-wire XTRONIC CVT. The new VC-Turbo gasoline engine is able to change its compression ratio from 8:1 to 14:1, or anything in between depending of the driving situation; whether there is need for top-end power or turbodiesel-like torque from low revs, or optimized fuel economy. The pistons' reach is continuously adjusted by an electric "Harmonic Drive" motor, which controls a multi-link system, affecting the top-dead-center of the pistons and changing the compression. The engine can also switch between efficiency-maximizing Atkinson cycle and regular combustion cycle, on the go – and there's both multipoint injection and gasoline direct injection employed. The result is 268 horsepower at 5,600 rpm and 280 pound-feet of torque at 4,400 rpm; good figures for a 2.0-liter four-cylinder gasoline engine with a single-scroll turbocharger. Infiniti says that the FWD version's fuel economy of 27 miles per gallon combined is 35-percent better than the previous-generation V6 engine; in AWD guise, it reaches 26 mpg, which is a 30-percent improvement. The new engine is pretty much all-aluminum, but the vaguely magical-sounding "transformative multi-link components" behind the variable compression system are made from high-carbon steel alloy. The engine's multi-link system also enables it to do away with any balancing shafts, and Infiniti compares its smoothness to a V6 rather than a regular four-cylinder. In addition to the aforementioned tech, the VC-Turbo engine has the world's first active engine mount vibration damping system to smoothen its operation even further. Related Video:

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.

Infiniti's QX Sport Inspiration is still attractive, in Paris, and now gray

Yes, crossovers tend to be boring. But this one is pretty! Then we remember it's going to turn into the front-drive-based QX50, so we automatically lose some interest. But the wheels will be driven by Infiniti's new VC-Turbo engine, which is kind of exciting! And for the 2016 Paris show, those wheels are bigger – 22-inchers in place of the 21s that the QX Sport Inspiration concept debuted with in Beijing earlier this year. (It's hard to tell a difference in the photos, but you can bet the imaginary ride of this concept will suffer, imaginarily.) The 22s are also painted bronze now along with the brake calipers, and the whole vehicle gets a coat of matte gray paint to replace the silver it was originally shown with. There's also some new brown leather in the previously very black and white interior. It's still pretty black and white, actually. Then there's the variable-compression-ratio VC-Turbo engine that will power the production QX50. We're getting a better look at this 2.0-liter four-cylinder turbo in cutaway form at the Paris show, and it continues to fascinate. It's a pretty neat thing, with a movable stroke position that allows it to vary the compression ratio between 8:1 for performance and 14:1 for efficiency (when the turbo isn't needed). That might not sound terribly cool, but it's a pretty big step forward in the march of efficient power. So yeah, crossovers can be boring, but at least this concept and the production car that will soon follow it have a few things going for them. Related Video: Featured Gallery Infiniti QX Sport Inspiration: Paris 2016 View 12 Photos Related Gallery Infiniti QX Sport Concept Related Gallery Infiniti QX Sport Inspiration concept for Paris View 10 Photos Image Credit: Live photos copyright 2016 Drew Phillips / Autoblog Paris Motor Show Infiniti Crossover Concept Cars Luxury 2016 paris motor show infiniti qx sport inspiration concept