Infiniti’s Brilliantly Downsized V-6 Turbo Shines

WardsAuto’s 10 Best Engines competition has recognized outstanding powertrains for 23 years. This installment of the 2017 “Story Behind the 10 Best Engines” series looks at the development of Nissan’s Infiniti brand’s potent new VR V-6.

It was a tough decision choosing the best of a flurry of new turbocharged V-6s hitting the market in 2017. One of the closest races was between very similar engines found in the Infiniti Q50 sedan and Q60 coupe and in the new Lincoln Continental and MKZ.

Engines from both brands displace 3.0L and pump out 400 hp. That kind of power makes them strong competition for naturally aspirated V-8s as well as several other premium 6-cyl. engines, including two versions of BMW’s creamy I-6 engine making 335 hp to 365 hp.

The Infiniti VR V-6 narrowly triumphed over the torquier same-size Lincoln for a 2017 Wards 10 Best Engines trophy due to better fuel efficiency and NVH characteristics.

The Infiniti V-6 is the first member of a new VR V-6 family developed exclusively for Nissan’s upscale Infiniti brand and is unrelated to the long-running (and multiple Wards 10 Best Engines award-winning) VQ V-6 family that still delivers strong performance in the ’17 Nissan Maxima, among other models. Built in Fukushima, Japan, it was launched first in the ’16 Infiniti Q50, replacing a 3.7L VQ V-6, then in the ’17 Q60. 

“With this new engine, we aim to achieve premium performance that is also fuel-efficient versus other 3.0L turbocharged engines,” says Chief Powertrain Engineer Shosaku Ando. “The development concept specifically called for sharp throttle response, outstanding output power and torque and excellent environmental performance in terms of fuel economy and emissions.”

The 3.0L “square” layout rivals competitive models while optimizing compliance with worldwide regulations. Only its 60-degree bank angle and 86-mm stroke are carried over from the 3.7L VQ V-6. A high-response electric-motor-driven intake-side variable valve timing (VVT) system replaces the latter’s continuously variable valve event and lift (VVEL) system.

Ando says the 400-hp engine achieves outstanding performance in comparison with competitors, is 0.7 seconds quicker from 0-60 mph (0-97 km/h) than the previous 3.7L VQ and also is very fuel efficient, achieving top-level brake specific fuel consumption among turbocharged engines.

The standard version is good for 300 hp and 295 lb.-ft. (400 Nm) of torque, while a high-output variant spins out 400 hp and 350 lb.-ft. (475 Nm). The primary differences are peak turbo boost, the latter’s turbo speed sensor and its extra electric water pump for charge cooling.

One of the development team’s toughest challenges was achieving such high output along with strong throttle response.

“The 400-hp high-output version uses a small diameter turbine with mixed-flow type blade and an intercept speed of 1,600 rpm to help it achieve both high power and sharp response.”

The team tested two turbochargers, one with a 39-mm (1.54-in.) diameter turbine and a 46-mm (1.8-in.) compressor; another with a 41-mm (1.6-in.) turbine and a 49-mm (1.9-in.) compressor. Limited by turbine speed, the smaller one topped out at 360 hp, while the larger unit delivered higher peak power but at the expense of torque response.

“To overcome this,” Ando says, “a turbine speed sensor system was developed that minimizes margins for overspeed prevention to allow the smaller turbine to be fully used to high operating speeds.”

Another major challenge was further reducing friction to simultaneously optimize performance and efficiency. “From the outset of development of the first-generation VQ engine, efforts were made to reduce friction, with additional measures being continuously applied over the years. In addition to applying these low-friction technologies to the VR engine, other measures also were adopted to reduce friction even further.”

These actions include using an electronically controlled variable-displacement oil pump, “diamond-like” carbon-coated piston top and oil rings, a hybrid piston skirt coating, 0W-20 low- viscosity engine oil and a new mirror cylinder bore coating technology, which uses arc spraying instead of the previous plasma spraying process.

“The spray nozzle is inserted inside the cylinder, and the bore is spray-coated as the nozzle is rotated and raised upward from the bottom,” Ando says.

This process achieves a smooth, mirror-finish bore surface that incorporates tiny air holes that retain oil without crosshatched grooves. Compared with the previous process, Ando says the resulting friction reduction is 21% at 2,000 rpm while overall internal friction reduction is 30% compared with the previous VQ37VHR engine despite addition of a vacuum pump and a high-pressure fuel pump.

One other huge challenge was recovering from the major earthquake that severely damaged Nissan’s Iwaki engine plant in Fukushima, Japan, in 2011. “We worked to quickly recover from that disaster,” he says, “and this VR engine is a symbol of the plant’s revival.”

Another key technology contributing to performance and efficiency is the electric VVT system. To achieve sharp throttle response with good fuel economy and clean emissions, the requirements for the VVT system include fast conversion, a wide conversion angle and the ability to convert flexibly to the optimum valve timing at engine start, Ando says.

Unlike hydraulic VVT, the electric system is unaffected by environmental conditions. It operates at engine start-up (before the first combustion) and throughout the oil temperature range; it can be changed immediately after start and attains its target angle within 0.5 seconds.

“This system provides a markedly higher conversion speed than the hydraulic VVT system,” he says. “In city driving, the Miller cycle with late intake valve closing timing is used for reducing pumping loss. The engine also can deliver high torque very quickly thanks to the large valve overlap produced by quickly converting to an early intake valve opening timing.”

A key design element is integrating the exhaust manifolds within the VR’s cylinder heads. It chops weight 11.7 lbs. (5.3 kg), reduces heat mass and improves NVH thanks to the short flow paths from cylinder head to catalyst. “And the optimized First Idle Retard (FIR) combustion allows the catalytic converter to heat up almost twice as fast as with a conventional engine, reducing cold-start emissions,” Ando says.

Another important feature is the water-cooled charge coolers that stabilize intake air temperature and enable the air path volume (from compressor to combustion chamber) to be reduced 60% (to 4.9L) compared with an air-cooled system, and contributes to sharper throttle response in all conditions.

Finally, Ando says the engine was designed from birth to be capable of meeting ever-increasing efficiency and emissions requirements with minimal changes, including retrofitting measures to vary precious metal loading of the emission control catalysts. “The regulations we targeted were the Super Ultra-Low Emission Vehicle (SULEV) standard in the U.S. and the EURO6c standard in Europe,” he says.

“In our testing, the 5-passenger Q50 topped 23 mpg (10.2L/100 km) for a number of editors,” says WardsAuto editor Tom Murphy. “Who needs a V-8 when this brilliant example of downsizing, combined with diligent efforts to reduce friction and vehicle weight, can allow a midsize sedan with six cylinders of motivation to move so swiftly, smoothly and effortlessly?”