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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.

Infiniti QX30 Concept is ready to join the compact crossover fray

Today, the compact crossover market is an automotive Klondike. Automakers are scrambling to stake their claim on an increasingly segmented, increasingly valuable landscape. That's especially true in the premium market, where every Audi Q3, BMW X1, Mercedes-Benz GLA, Lexus NX and Buick Encore sold takes up a piece of market share that requires a great deal of effort for another automaker, in this case Infiniti, to reclaim. That makes the new QX30 Concept, debuting this week at the 2015 Geneva Motor Show, an extremely important vehicle for the Nissan-owned brand. The QX30 Concept has already been "earmarked for production" and will be launched next year, according to Infiniti. When that happens, we'll see a compact CUV with toned down styling from the vehicle shown here, much like the upcoming Q30 production model. It's fair to say the looks of the QX30 are in direct opposition to those of the aforementioned Lexus NX. Where that car is sharp and angular, Infiniti's designers emphasized the "spontaneous and fluid" look of the new concept. Infiniti's most recent, Q50-inspired design language works nicely in a compact CUV form factor. The double-arch grille and its flanking headlights give the QX30 a refined, almost predatory look. That, as it turns out, is intentional. "The Q30 Concept was like a panther, lithe and slender. We transformed the QX30 Concept into a mountain lion, strong and muscular," Infiniti's Executive Design Director Alfonso Albaisa said in a statement. The strong, wavy character lines in the profile lead into the short, chopped rear overhangs. Above the beltline, the rear window is raked forward aggressively, lending the QX30 a coupe-like profile. In the cabin, we can already see the makings of a production car's interior, with two strong material choices – dark brown and blue leather – highlighting the dash. On the concept, purple accent lighting is emitted from the center stack's controls, while the violet shade carries over into what looks like a digital instrument cluster and the speaker surrounds in the doors. Sections of quilted leather on the seats, meanwhile, look very nice, but we doubt they will make it to production on what is ultimately going to be a reasonably priced vehicle.

A look inside Infiniti's variable-compression engine

We're sympathetic to anyone who had trouble understanding what's going on with Infiniti's new variable-compression engine. While we got a full tech briefing on the novel VC-Turbo back in August, the visual aids were lacking. The cutaway engine Infiniti brought to the Paris show fixes all of that. You can thank the little green and pink lines on the cutaway for making the whole idea a little more clear. Click through the gallery to see two lines – one green and one pink – that represent the different strokes allowing for different compression ratios. Remember, the compression ratio is the amount of volume in the cylinder on intake compared to the amount at the end of the compression stroke. Leave more room at the end and you lower that ratio. The length of the stroke doesn't change with this system, but where it sits along the cylinder does. Hence those two lines. The variable compression ratio allows this new turbocharged engine to maximize fuel economy when the turbo isn't needed by raising the compression ratio. It will see its first use in the next Infiniti QX50 crossover, previewed by the QX Sport Inspiration concept that's also on display in Paris, and has performance targets of 268 horsepower and 288 pound-feet of torque. After, it will migrate to other Infiniti and Nissan vehicles, with transverse front-drive-based applications first in line. Eventually, it's likely to completely replace Nissan's corporate 3.5-liter V6. We'll be poking around the engine a little more in Paris today to try and get some more info. For now, enjoy those cutaway images and those friendly little lines. Featured Gallery Infiniti VC-Turbo engine cutaway View 14 Photos Paris Motor Show Infiniti Nissan Technology Emerging Technologies engine 2016 paris motor show