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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.

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

2014 Infiniti Q50

Avoiding An Identity Crisis... For Now
Infiniti is a brand that has been quietly undergoing major upheaval - and not just with the numbers and letters on its trunklids. Back in December, Nissan's premium brand rankled fans and pundits by announcing it would redo its alphanumeric nomenclature, yet that decision was but a PR speedbump - there are bigger fish to fry. After all, this is a marque that was on the chopping block just a couple of years ago, and now it has a major opportunity to succeed thanks to new investment, new independence (Infiniti is now responsible for its own design, engineering, marketing, quality and human resources), a new global headquarters in Hong Kong, and new marching orders from new leadership that calls for a revitalized and expanded portfolio.
Yet if you think that the Q-based naming convention is the first sign of the brand's new direction, you might have missed Infiniti's biggest signal flare: the 2013 JX crossover. Fine premium three-row crossover that it may be, it's still the first Infiniti in ages that operates without a scintilla of driving entertainment at the core of its genetic makeup. (The last - and perhaps only - previous example was also Pathfinder-based, the 1997 QX4). To be fair, three-row CUVs have a laundry list of priorities before driving enjoyment figures in, but the message the JX (henceforth known as the QX60) sends is clear: Infiniti is going after more segments and more customers. Plans are afoot to expand the company's product line by a whopping 60 percent over the next five years, and in short, that means Infiniti is no longer content to be the unsung Japanese BMW - it needs vehicles that satisfy a wider swath of consumers. Despite all this, Infiniti officials we spoke with were keen to assert that driving pleasure remains very much core to their mission, and to that of this 2014 Q50 in particular.