There’s a new kind of engine under the hood of the new Infiniti QX50. Like many of its competitors, it’s a turbocharged 2.0-liter inline-four, but what goes on inside is radically different from anything that has come before it. For the first time in a production vehicle, there’s an engine that can change its compression ratio and even its displacement (a tiny bit), a project that, according to the company, has taken more than 20 years. Why bother? Varying the compression ratio promises to maximize efficiency whether you’re cruising at part throttle or running toward the redline on 22.0 psi of boost.
Infiniti’s VC-T engine (for Variable Compression, Turbocharged) can change how far its pistons rise in its cylinders, which changes the engine’s compression ratio, a parameter that, heretofore, had been fixed. Infiniti’s engine can bump the compression ratio from a low of 8.0:1 to a high of 14.0:1. Changing an engine’s stroke usually requires a new crankshaft. Instead, Infiniti’s engine introduces a joint between the crankshaft and the connecting rods, and moves the joint with a computer-controlled arm. In the process of changing how high the pistons move, the mechanism incidentally varies the stroke by 1.2 mm, which causes the engine’s displacement to vary slightly—from 1971 cc (14:1) to 1997 cc (8:1).
It’s telling that no one has done this before. Adding extra pieces to a high-stress and critical component like a crankshaft is like slipping erector-set parts between your vertebrae. As you’d expect, the additional heavy-duty components add mass—about 22 pounds—to the moving parts of the engine, but the design moves the crankshaft off-center, smoothing out the piston’s motion. Unlike many inline-four engines displacing 2.0-liters or more, the Infiniti engine doesn’t use balance shafts, which helps offset the weight of the new parts. Dynamic engine mounts keep any bad vibes from getting inside the cabin.
A Small Victory
Given that the aim of all this monkey motion is improved efficiency, how good is the resulting fuel economy? Final EPA numbers are still pending, but the preliminary estimates are 24 mpg city and 30 highway for an all-wheel-drive model, yielding a combined figure of 26 mpg. Front-wheel-drive versions are expected to do 1 mpg better in the highway test, bumping the combined number to 27 mpg.
The good news is that Infiniti beats all of the 2.0-liter turbo fours in its segment. Bad news? This isn’t an end-zone-dance win. Comparing to their AWD versions, the QX50 bests the combined number of the 2.0-liter-powered Audi Q5 and BMW X3 by 1 mpg. A win is a win though, and who doesn’t love a good Rube Goldberg machine?
Luxury-minded customers are more likely to care about how the QX50 looks parked in front of their houses. Its exterior design clings closely to the class norms, which means it treads the line between handsome and dull—just attractive enough to get the neighbors to notice, but not so striking that it inspires them to knock on your door. Infiniti designed some distinction into the D-pillar shape, but many details, such as the headlights and taillights, could’ve been pulled from an Acura or Mazda.
The interior doesn’t take many risks, either. Material quality is excellent, and the quilted leather seats and microsuede trim on the door panels and center console are elegant touches, but these niceties are only available on the top trim level. In the center stack, two touchscreens divide the infotainment labor. The upper display is for the navigation system, one that we should mention appears to have been pulled right out of a 2008 Infiniti. Below that display is another touchscreen that has apps, audio controls, phone pairing, vehicle settings, and destination entry. Will it bother you that the two graphic displays don’t share the same fonts? It bothers us. At least the climate controls are traditional buttons that flank the lower screen.
The cabin is wide and there’s a sense of space and airiness that transcends the QX50’s compact segment. In fact, the QX50’s new platform makes it wider than the Lexus RX350, and the sliding bench rear seat boasts more legroom than the one in the longer Lexus. Along with the soft and soothing front seats, the QX50 has more than enough space to comfortably accommodate four six-foot passengers.
Drives Like It Looks
Driving the QX50 is analogous to looking at it. It’s refined and inoffensive. The transverse-engine layout leads to predictable, if uninspiring dynamics. Body motions are tight, and it reliably goes where it’s pointed. Point harder and the front tires give a clear warning that they’re running out of grip. Infiniti hasn’t given up on the steer-by-wire system that’s available on the Q50 and Q60—it’s here in the QX50, too. Efforts are light, and there’s a weird artificialness in the way it increases efforts when the front tires are stressed, but the steering is very quick and lively off center.
Pulling away from a stop, there’s what feels like a hint of turbo lag. Some of the hesitation may be due to the continuously variable automatic transmission’s sluggish responses and throttle tuning. Despite the occasional hesitation and springiness of the CVT, the engine provides real punch. All 280 lb-ft of torque are available from 1600 rpm and the 268 horsepower come in at 5600 rpm. In most driving, there’s enough torque and power to keep the CVT from having to spin the engine past 3000 rpm. Should you want to venture into the tachometer’s upper reaches, Infiniti claims a believable zero-to-60-mph time of 6.2 seconds for the AWD version and 6.7 for the front-driver.
In normal use, there’s nothing remarkable or unusual about how the QX50’s engine responds to throttle inputs, which, considering what’s going on inside, is itself remarkable. A digital meter labeled Power and Eco that sits between the speedometer and tachometer is the only telltale when the engine is in high-compression or low-compression mode. We did notice a delightfully rorty, almost Italianate sound as the engine approaches its 6000-rpm redline. It’s a welcome personality trait in an otherwise quiet and refined vehicle.
Few owners are likely to keep the QX50’s accelerator pedal floored for very long, but if they do they’ll notice that the CVT mimics gear shifts to avoid having the engine bawling at a fixed, high-rpm under acceleration. Grab a paddle shifter and the CVT offers up 8 preset ratios for QX50 customers who miss clearly defined gears, a number that probably rounds to zero. There are four selectable driving modes: Eco gives the throttle pedal an epidural and removes all sensitivity, switching to Sport keeps the CVT at the ready by keeping engine revs elevated and the throttle awake, and Standard mode dials back the throttle response slightly and puts the CVT into a low-revving fuel-saving mode. Finally, a Personal mode lets the driver choose their own mix of settings.
Pricing starts below $40,000 for the base Pure trim with front-wheel drive and can exceed $60,000 for a fully loaded QX50 in Essential trim with all-wheel drive (an $1800 upgrade at all three trim levels). The new crossover enters a growing and massive segment in which it will face tough competition from established players such as the Acura RDX, Audi Q5, BMW X3, Cadillac XT5, Lexus NX, Mercedes-Benz GLC, and Porsche Macan.
Will QX50 buyers really care that the engine is the first of its kind and a technological triumph? Probably not much. What will sell them on the QX50 are its promises of fuel economy, luxurious appointments, build quality, interior space, and inoffensive style. Provided that the engine doesn’t pull an Oldsmobile diesel or a Cadillac V-8-6-4, the unique complexity and novel solution under the hood will go unnoticed, and that’s not the applause that the engineers deserve.
