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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's QX50 Concept debuts in oh-so-close-to-production form in Detroit

Infiniti debuted the new QX50 concept today at the Detroit Auto Show, a preview of the midsize crossover set to hit the market soon and an evolution of the 2016 QX Sport Inspiration. This previews the followup to the current QX50, which debuted way back in 2007 as the Infiniti EX. The QX draws on Infiniti's current design language and looks like a slightly shortened version of the larger QX60. While this is still a concept, don't expect the full production version to stray too far from what we see here. Infiniti's press release is full of phrases like "driver-centric, passenger-minded" design, but in reality it's just a handsome but mostly traditional shape. The big news is that the QX50 will be the first application of Infiniti's trick variable-compression 2.0-liter turbocharged inline four. The engine's design promises both high horsepower and high fuel economy. Infiniti is claiming 268 horsepower and 27-percent better fuel economy when compared to the outgoing model. View 17 Photos Also coming on the new QX50 are a suite of active safety and autonomous features. While the details on both are extremely vague, Infiniti claims that the autonomous tech will allow the driver to retain ultimate control over the vehicle. That seems a bit counter to how autonomous driving works, so it will be interesting to see how the system actually functions. The active safety systems are said to be proactive, with future versions using lasers, radar, and cameras. While the outgoing QX50 was a rear-wheel-drive swoopy crossover, this new model appears to send power to the front wheels. Infiniti's release doesn't expressly say, but it does hint towards it with notes about a shorter hood and a "front-biased intelligent all-wheel drive system." This makes sense, and we don't see many enthusiasts lamenting the loss of a dated, rear-drive crossover. No word on pricing or when we'll actually see a production version. The current model turns 10 this year, albeit with a mid-cycle refresh. Look for news of a final production version very soon. Related Video: This content is hosted by a third party. To view it, please update your privacy preferences. Manage Settings. Related Gallery Infiniti QX50 Concept View 24 Photos Image Credit: Live photos copyright 2017 Drew Phillips / Autoblog Design/Style Detroit Auto Show Infiniti Technology Emerging Technologies Crossover SUV Concept Cars Videos Original Video 2017 Detroit Auto Show infiniti qx50 variable compression ratio

The yin and yang of the 2017 Infiniti Q50 Red Sport 400

When we first drove the Q50 Red Sport 400, Infiniti had the car out at a prepared slalom-and-cone course in a large, open parking lot. The car was stacked up against another Q50 without the Direct Adaptive Steer steer-by-wire system, and the course was designed to show that the DAS-equipped Red Sport 400 (it's a $1,000 option) required less steering input to master the same course. With all due respect to Infiniti, which is invested in this unfortunate system and has been working hard to revise it, the comparison doesn't make a lot of sense. The non-DAS Red Sport 400 has a steering ratio of 15:1 in RWD and 16.7:1 in AWD forms. The DAS system can vary between 12:1 and 32.9:1 in RWD and 11.8:1 to 32.3:1 in AWD flavors. At its extremes, the DAS system's ratio is vastly different than the fixed-ratio cars. So sure, with a super-quick steering ratio available, the DAS driver's going to do less work. It's all in the gearing. Does this mean it's better, that the steering feel is more natural, that it's easier to hustle quickly? The amount the driver saws at the wheel isn't an indication of that, necessarily. After a few days in a rear-drive Red Sport 400, I'm saying that the spooky disconnection between the driver and the front wheels would be a severe deficit to a driver on a real autocross course. It's not like the DAS system is choosing bad ratios within its range, it's just not supplying the feedback to make it enjoyable. Knowing what your front tires are up to is critical. I can hear you saying right now, "But what Q50 Red Sport 400 owners are going to autocross their cars?" Sure, but it was just a means to an end: showing off the DAS in a good light. And in that case, it probably did. The thing is, in isolation, not back-to-back with a non-DAS car with a slow steering ratio, the DAS system has the same issues it's always had: It simply doesn't feel natural. It doesn't feel intuitive. There doesn't seem to be any real advantage over a slightly quicker rack. I don't hear about people making buying decisions based on how much work they have to do sawing at the wheel, do you? So, that's one side of the Q50 coin – one that's hard to ignore if you're an enthusiast and steering feel is an important connection between you and the vehicle you just dropped a large hunk of change on, and will be spending a lot of your time in. The other is that there's a really compelling reason to drive a Red Sport 400: The 3.0-liter, twin-turbocharged V6 is a monster.