Nissan VQ Enjoys 14 Years of Accolades

The Ward’s 10 Best Engines competition celebrates 14 years of recognizing outstanding powertrain development. In this installment of our 2008 series, Nissan explains the technology behind the only engine making the list all 14 years: the supremely smooth VQ V-6.

When Nissan Motor Co. Ltd. engineers kicked off design of an all-new V-6 family 18 years ago, they planned to make it at least the equal of any, and better than most. They could not have predicted how powerful, popular and prolific it would be nearly two decades later.

GM has its legendary small-block V-8, BMW its silky in-line six, VW/Audi their mighty mite turbo four. Now Nissan has its signature VQ V-6 powering nearly everything it makes midsize and up.

Together with bold, distinctive vehicle styling, the VQ also arguably powered the company’s comeback from the brink of bankruptcy earlier this century, at least in the U.S. And it has earned a Ward’s 10 Best Engines trophy every year since the competition began 14 years ago.

The first all-aluminum VQ V-6 debuted in 1994 in 2.0L, 2.5L and 3.0L displacements, the latter bringing 190 horses and 205 lb.-ft. (278 Nm) of torque to new U.S.-market ‘95 Nissan Maxima and Infiniti I30 sedans.

The V-6 was relatively light and compact, with lightweight internal parts, micro- finished camshafts and crankshaft, molybdenum-coated pistons and a clever 2-way feature that cooled its heads and block separately to enable the block to warm up more quickly for reduced emissions.

Four years later, a “1st Evolution” 3.0L VQ upped the ante to 222 hp and 217 lb.-ft. (294 Nm), with variable-inertia intake manifold runners and a variable backpressure muffler.

The U.S. engine’s power peak was up to 6,400 rpm from the previous 5,600, and direct-injection gasoline (DIG) enhanced the fuel economy of Japanese-market 2.5L and 3.0L versions.

“Japan was very much focused on fuel economy at that time, while the U.S. fuel price was still very low,” says Nissan Technical Center North America President Motohiro Matsumura, who was engineering manager for the “2nd Evolution” VQ engine that debuted in 2001.

That 2nd Evolution brought a high-stiffness cylinder block, a 10.3:1 compression ratio and new technology that included continuous valve timing control (CVTC), a variable resonance intake chamber, an electronically controlled throttle chamber, a “noiseless” timing chain and long-reach platinum-tipped spark plugs.

Despite a displacement increase to 3.5L and output boosts to 255 hp and 246 lb.-ft. (333 Nm) of torque, the U.S. VQ35 V-6’s fuel efficiency was similar to that of its smaller, lower-power predecessor.

The first longitudinal rear-wheel-drive VQ35 powered the ’01 Nissan Pathfinder, and U.S. front-drive applications expanded for ’02 to an all-new midsize Nissan Altima in addition to the Maxima and Infiniti I35.

As Nissan’s turnaround hit high gear for 2003, the VQ proliferated into a plethora of new products: the high-style Murano cross/utility vehicle and new 350Z sports car for ’03; and a new Quest minivan, Infiniti G35 coupe and sedan and the aggressive Infiniti FX35 CUV for ’04. The next year brought a 4.0L VQ40 for the Pathfinder SUV, and a new Infiniti M35 sedan got the 3.5L for ’06.

“After 2002, the volume was remarkably high,” Matsumura says. “Two years later, Toyota introduced a 3.5L, Honda introduced a 3.5L, and we were in a power war in the U.S.”

So 2006 brought a new VQ35HR (high-revolution) variant for the ’07 350Z and G35 sedan with a 10.6:1 compression ratio and twin CVTC, which used electromagnetic actuators to vary exhaust-valve timing.

Delivering 306 horses at 6,800 rpm and 268 lb.-ft. (361 Nm) at 4,800 rpm, this smooth and sonorous revver also boasts symmetrical dual intake and exhaust systems with equal-length exhaust manifolds, low-friction asymmetric piston skirts and “diamond-like carbon” (DLC) valve lifters and long-reach iridium spark plugs.

“We wanted to increase rpm to (enable the engine to) work better with the manual transmission, especially for the 350Z,” Matsumura explains. “We redesigned the structure and increased the block height to use longer connecting rods, which reduces their angle for lower friction.

“Electromagnetic actuators twist the exhaust cam phasers to increase overlap. The very hard, ultra-low friction DLC-coated lifters are familiar in U.S. dragster and oval racing engines. The piston pins were also DLC coated to reduce friction, and reduced-diameter spark plugs improve cylinder-head cooling.”

That brings us to the 2008 10 Best Engines list, on which a bigger and better VQ resides. The higher-tech and otherwise much-improved 3.7L VQ37VHR (VVEL high-revolution) V-6 that powers Infiniti’s sleek new ’08 Infiniti G37 coupe.

This newest VQ family member pumps out a muscular 330 hp at 7,000 rpm and 270 lb.-ft. of torque (366 Nm) at 5,200 rpm, and it also soon will motivate an ’09 G37 sedan and the new 370Z sports car coming this fall. According to Nissan, 35% of its parts are new.

With the lofty goals of best-in-class performance, cleanest-in-class emissions and real-world fuel-economy improvement over the VQ35HR, Nissan’s engineers began with new VVEL (Variable Valve Event and Lift) on the intake side, a less complex execution of the same idea pioneered by BMW’s Valvetronic system. VVEL continuously varies intake valve lift to control the amount of mixture entering the cylinders, relieving the throttle of that responsibility.

As a result, it substantially reduces pumping losses, especially during constant part-throttle conditions, and camshaft friction (due to lower lift) while improving throttle response and torque by optimizing valve open/close movements.

The system also stabilizes combustion, even when the engine is cool, and increases exhaust temperatures to more quickly warm the catalyst. Combined with improved CVTC (now with an ultra-wide phase angle), this helps achieve LEV2-ULEV emission standards with less dependency on the catalytic converter.

“We started development of this new technology in 2004,” Matsumura says. “It makes a no-throttling engine. When the valve lift is very small, the engine does not throttle the intake air, which reduces pumping losses – like a diesel engine – for much better fuel economy and cleaner emissions.”

Other updates include extended cylinder block liners to accommodate the longer stroke; higher-flow resin collector, intake manifold and exhaust ports; thin-section intake valve “umbrellas” for improved flow; and a ladder-frame camshaft bracket for higher rigidity. “Most of the noise from the cylinder head came from vibration of the cam carrier,” Matsumura explains. “The very strong valve springs were actually bending the camshaft.”

Development challenges with the latest VQ were many. “In my experience on the second generation,” Matsumura says, “one major challenge was deciding how best to increase rigidity of the block to reduce vibrations. Combustion design and design of the moving parts to reduce friction also were challenges. And the DLC was developed for this engine.”

What about potential future improvements to boost fuel economy?

“I can’t tell you today what we will do,” he says. “With CAD simulations, it’s easy to check the deformation of a part, for example, and how much force it takes to deform it. Friction, combustion and other key elements also can be simulated in the computer, which makes improvement relatively easy. But the last 10% can be very challenging. Direct injection is one of the cheaper technologies [we can use], but with any direction to improve fuel economy, any technical solution, we have to preserve the DNA.”

Built in Iwaki, Japan, and Decherd, TN, Nissan’s versatile VQ V-6 is fast approaching an annual volume of 4 million for worldwide applications. Which raises the obvious but uncomfortable question: with V-6s this good, who really needs a V-8?