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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.

Autoblog Podcast #344

Doug DeMuro from Plays With Cars, Infiniti Q50, Subaru BRZ STI, Porsche Macan
Episode #344 of the Autoblog podcast is here, and this week, Dan Roth and Executive Editor Chris Paukert are joined by Doug DeMuro, author of Plays With Cars and prolific internet autowriting presence. Topics include the latest spy shots of the Porsche Macan, the 2014 Infiniti Q50, and the teaser images we've recently seen of a Subaru BRZ wearing STI badges. As always, we start with what's in the garage and finish up with some of your questions. For those of you who hung with us live on our UStream channel, thanks for taking the time. You can follow along after the jump with our Q&A. Thanks for listening!
Autoblog Podcast #344:

Infiniti previews its own Vision Gran Turismo

Every automaker and its parent company is lining up to design its own set of wheels for the GT6 as part of the Vision Gran Turismo program, and this latest one comes from Infiniti. Although nothing in the way of details were disclosed at this point, the two teaser images released today show that, like most of its compatriots, Infiniti's design is for a low-slung, track-focused, two-door sports car. Its long bonnet suggests a front-engined layout, with an intriguingly ovoid windshield framed by raised buttress A-pillars and Infiniti's signature dog-leg rear pillars. The aerodynamic profiling looks suitably advanced for a mythical beast like this one, with deep extractor vents cut into the hood, intersecting side sills running from the front brake vents, an enormous rear diffuser and an even bigger rear wing. More than that we couldn't tell you at this point, but we're sure video racers will enjoy driving this super-Datsun as much as the Nissan Concept 2020 Vision Gran Turismo released back in June.