YOKOHAMA – Nissan Motor Co. Ltd., in introducing the all-new Infiniti G35 sedan in October, also unwrapped its new VQ35HR V-6 – with HR standing for “high response” and “high revolution.”

This latest 3.5L DOHC V-6, which Nissan engineers are calling the fourth generation of the VQ modular engine family introduced in 2004, also is to be installed in the Nissan 350Z next spring.

In Infiniti G35 specification, the VQ35HR produces 306 hp at 6,800 rpm and 268 lb.-ft. (363 Nm) of torque at 5,200 rpm, while achieving California LEV II emission standards in the U.S. and Ultra-Low Emissions Vehicle certification in Japan.

And it is quiet – with noise consistent and measured during acceleration and through the entire engine speed range, says Atsuhiko Hayakawa, program director of Nissan’s V-6 and V-8 engine development group, calling the new VQ35 HR’s sound signature “stable, clear and linear.”

Hayakawa says the VQ35 HR’s primary new design feature, when compared with previous VQ units, is that it can be installed in front-, all- and rear-wheel-drive vehicles, although for the time being it is available only in RWD models.

For RWD cars such as the Infiniti G35 (the export version of the Nissan’s home-market Skyline) and 350Z, the engine is mated to either a 6-speed manual or 5-speed automatic transmission. The automatic gearbox features a “downshift rev-matching” feature to avoid driveline shock during sporty downshifts.

For FWD vehicles such as the Murano cross/utility vehicle and the U.S.-built Altima and Maxima sedans, Nissan backs the VQ with a continuously variable transmission as the “automatic” transmission.

The auto maker produces the new VQ35HR in Japan at its Iwaki plant in Fukushima Prefecture. This is handy because most Infiniti models, not to mention the 350Z, are built nearby at its Tochigi plant in northeastern Japan.

However, VQ engines for the auto maker’s FWD lineup, including the Altima and Maxima, both built in Smyrna, TN, are produced 75 miles (120 km) away at Nissan’s Dechard engine plant in eastern Tennessee.

Hitachi supplies the engine’s 32-bit engine control unit.

    Other features of the new, fourth-generation VQ:
  • For both the VQ35HR and VQ25HR (a 2.5L variant not used in the U.S.), fuel efficiency was boosted 10% over the VQ35DE and VQ25DD, as measured by Nissan’s “daily use” test standard.
  • -Both engines accelerate the vehicles in which they are fitted from 0-62 mph (100 km/h) one second quicker than their predecessors. Hayakawa says the engine is best in class for acceleration but not fuel economy, where the direct-injection gasoline 3.5L DOHC V-6 for the Lexus IS350 is slightly better.
  • The VQ35HR uses 80% new parts while the VQ25HR carries over roughly half. Included among new components: the cylinder block, cylinder head, front cover and oil pan. Among the principal carry-over parts: hoses.
  • The engine employs the world’s first hydrogen-free, “diamond-like” carbon-coated valve lifters. Result: a 40% reduction in friction at this critical surface. The VQ is Nissan’s first engine to adopt the DLC technology.
  • To suppress exhaust backpressure, engineers developed equal-length exhaust manifolds that begin a dual-exhaust system that is symmetrical all the way to the exhaust tips.
  • To improve fuel economy, the engine employs some 40 new and improved technologies, including iridium spark plugs, early activating air-fuel sensors, ultra-low heat mass catalysts and atomizing fuel injectors.
  • =In addition, engineers adopted a dual-path intake, a first for Nissan. Employing hydraulically actuated continuously variable valve timing for the intake cams and an electromagnetically actuated cam phaser on the exhaust side, the system offers a high degree of flexibliity in setting valve timing to improve combustion efficiency over a wide engine speed range, Hayakawa says.
    Other fuel-saving features include a higher compression ratio, asymmetric-skirt pistons that reduce friction, low-friction piston rings, a long-discharge ignition coil and twin knock sensors.
  • GTo improve performance and reduce vibration and noise, Nissan raised the cylinder block deck height 0.33 ins. (8.4 mm) while keeping the same 3.2-in. (81.4-mm) stroke as the previous 3.5L VQ. To compensate, engineers extended the length of the connecting rod by 0.29 ins. (7.6 mm). Hayakawa says the new higher deck and longer connecting rods help to minimize piston inclination and reduce friction.
    The auto maker also introduced a narrower, asymmetric piston skirt; on the side of the piston that sees the smaller amount of side forces, the skirt is shorter, resulting in a 7.6% friction reduction.
    Another major addition is a ladder-frame structure for the lower cylinder block to markedly improve overall engine stiffness, thereby minimizing vibration at the higher engine rpm for which the VQ35HR was designed, says Hayakawa.
  • The VQ35HR employs a timing chain, not a timing belt.
  • dMain suppliers include Calsonic Kansei Corp. (exhaust manifold and other exhaust system components); Denso Corp. (atomizing fuel injector); Hitachi Ltd. (intake valve timing controls and pistons); Hitachi Metals Ltd. (intake manifold); Nittan Valve Co. Ltd. (exhaust valve timing controls); and Riken Co. Ltd. (diamond-like carbon-coated cam-valve lifter).

Hayakawa says the fourth-generation VQ V-6 will have a 5-year life span before the next series of refinements. However, he says the engine cannot be adapted for diesel operation – but could be incorporated into a hybrid-electric vehicle drivetrain.

The executive declines to estimate global demand for V-6s but warns, “No one wants 4-cyl. engines for premium cars.”

He says only Nissan offers a 2.5L V-6 for FWD home-market models such as the Teana.

With the addition of a new $87 million machining line at its Iwaki plant, Hayakawa expects VQ engine production in Japan to reach 46,700 units per month and 560,000 annually. He expects Dechard output to almost match that level with small volumes of VQ production – less than 2,000 units per month – built at Nissan-affiliated plants in Thailand and Taiwan.

He indicates the VQ family, although not necessarily the HR version, is being considered for certain models made by Nissan partner Renault SA.

In Nissan models, various versions of the engine series (including the VQ20DE, VQ23DE, VQ25DD, VQ25DE, VQ30DE, VQ30DET, VQ35DE and VQ40DE) are installed in the Presage, Murano, Frontier, Navara, Pathfinder, Stagea, Elgrand, Xterra, FX35, FX45, M35, M45 and Fuga, along with the Altima, Maxima and Teana.

The Japan-market Skyline, G35 and 350Z are the only models currently earmarked for the new HR variant of the VQ modular engine family.

The VQ has been the only engine to win a Ward's 10 Best Engines award every year, including the latest round for 2007, since the competition's inception in 1995.