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Nissan VQ Still Leads V-6 Pack

Continual updates keep Nissan’s formidable VQ V-6 at the front of the pack after four generations. The new 3.7L iteration is rated at 330 hp.

The Ward’s 10 Best Engines competition celebrates 13 years of recognizing outstanding powertrain development. In this eighth of a series, Ward’s delves into the development process behind Nissan’s benchmark VQ V-6. Watch for features on the other 2007 winners throughout the year.

Thirteen years and four generations after its U.S. launch for the ‘95 model year, a single word summarizes the enormous impact of Nissan Motor Co. Ltd.’s VQ architecture: benchmark.

Don’t ask us – although we think 13 consecutive years of Ward’s 10 Best Engines awards is a certain implicit endorsement.

No, ask anyone. They don’t have to be in the powertrain sector, or even in the auto business. Anyone with any octane in their veins knows Nissan’s VQ is the gold standard of V-6s.

Introduced as a 3.0L 60-degree DOHC architecture, specifications for the first VQ – 190 hp and 205 lb.-ft. (278 Nm) of torque – were healthy but not necessarily overwhelming in its day. But the VQ’s design brief – an attack on friction, mass and noise, vibration and harshness – made the VQ wholly special.

The execution was highlighted by a microfinished crankshaft and camshafts, a fairly radical manufacturing trick for high-volume engines. The VQ’s valvetrain was a remarkable 20 lbs. (9 kg) lighter than that of the iron-block 3.0L V-6 the VQ replaced, and the entire engine more than 108 lbs. (48 kg) lighter.

The VQ became a benchmark not because it was muscle-bound, but because of brilliant throttle response, and it revved more effortlessly, more blithely, than any V-6 before.

Successive VQ generations brought variable valve timing, a displacement increase to 3.5L (’02), a less-convincing 4.0L light-truck variant (’05) and myriad structural and component upgrades mixed in along the way.

For this year, Nissan engineers promised a major upgrade. It was presented in the form of the VQ35HR, for High Response and High Revolution. Yes, even more revs (and refinement, by the way) from an engine for which free-revving was a prime attribute.

Engine enhancements for the new fourth generation include a crankcase ladder frame, a new cylinder-bore design and specially extended connecting rods.

The new VQ35HR’s performance has been markedly upgraded as well: The redline is extended to a delicious (and productive) 7,500 rpm.

Also contributing to the new power and refinement enhancements are a higher compression ratio (10.6:1 vs. 10.3:1 for the third-generation VQ35, which remains in service in some applications), straighter intake runners and a symmetrical twin intake-plenum design, as well as exhaust manifolds incorporating three equal-length pipes.

All the attention to the intake and exhaust routing, Nissan engineers say, came from the goal of achieving a more emotional sound when the engine revs, and a linear sound that correlates to throttle opening and acceleration rate.

They present scatter-chart evidence that shows an improvement in clarity of “desirable” sound and a reduction in high-frequency noise. They add that the design changes reduce intake “resistance” by 18%.

Because of the required change in deck height (height of the engine block from crankshaft centerline to the top of the bare block) for the new VQ35HR, a second plant was constructed at the company’s highly automated Iwaki engine facility in Japan.

Happily, but not coincidentally, the changes for the new fourth-generation VQ also result in approximately 10% better fuel economy, according to Nissan’s figures.

Engineers say the improved efficiency is due largely to the advanced initiatives to further reduce friction in what already is an engine layout designed with low friction in mind. The previously mentioned longer connecting rods attach to asymmetrically skirted pistons to reduce side forces on the piston, and other measures also cut friction.

But Nissan engineers are particularly proud of one unique new component, seemingly innocuous but industriously clever: a new “hydrogen-free diamond-like carbon” (DLC) treatment of the valve lifters that reduces friction with the rocker arm.

This nano-technology, says Nissan, allows the coating to better bind with the engine oil, creating a durable film on the surface of the valve lifter that cuts friction by 40%. Nissan technical material suggests other engine surfaces – specifically, piston rings and piston pins – are potential targets for the DLC treatment, which the company says eventually could reduce overall engine friction by 25%.

Nissan says that, along with oil-incorporating special additives, the VQ35HR is the world’s first application of the technology.

Next for the VQ V-6 is the enlargement to 3.7L, already launched this year for the all-new Infiniti G37 coupe. Where the VQ35HR currently tops out at 306 hp, the new 3.7L displacement is rated at 330 hp.

Apart from the displacement bump, a major boost comes from the all-new VVEL (Variable Valve Event and Lift) enhancement to the existing Continuous Valve Timing Control (C-VTC) variable valve timing system.

The VVEL hardware enables continuous variability of intake-valve lift, essentially permitting the engine to be throttled via the intake valves.

The system, similar to others in production, such as BMW AG’s Valvetronic, markedly reduces engine pumping losses typical in light-throttle engine operation, where the engine must “pull” against a mostly closed throttle.

Nissan likens the effect to pulling a syringe: A large, wide syringe is much easier to pull than a thin one.

In addition to improved efficiency, particularly in light-throttle driving, Nissan engineers say the VVEL system enhances responsiveness by reducing the delay between when the driver depresses the accelerator pedal and when intake air can enter the cylinders.

They also claim improvements in torque delivery and a reduction in emissions because of higher intake velocities and quicker heating of the catalysts.

There appears to be merit to the claims, as the new 3.7L VQ, despite its power increase of nearly 10% over its 3.5L counterpart in the outgoing Infiniti G35 coupe, produces a 1 mpg (0.42 km/L) improvement in the Environmental Protection Agency city and highway driving cycles.

And this despite the fact the new EPA fuel-economy tests and ratings, adopted for ’08 models, are known to produce less-generous figures in most situations.

Nissan engineers will not say if the VVEL system will be adopted for the more widespread 3.5L variants of the VQ V-6.

Ward’s will test the new VVEL-equipped 3.7L VQ variant, as well as 2007’s award-winning VQ35HR, for the 2008 Ward’s 10 Best Engines competition.

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