The Ward's 10 Best Engines competition celebrates 14 years of recognizing outstanding powertrain development. In the fifth of our 2008 series, Ward's looks at the design philosophy behind Toyota's 3.5L DOHC V-6.

What Would You Call an Engine with Two complete fuel-injection systems? Dualjection? Twinjection? Most good marketing mavens could come up with something sexy.

Then again, some might call it expensive overkill. Redundant. Belt and suspenders.

Toyota Motor Corp. modestly calls it 2GR-FSE. That means it's the No. 2 member of the GR family of DOHC, dual variable-valve timing “with intelligence” (VVT-i), 60-degree aluminum V-6s; which happens to displace 3.5L and use direct gasoline injection (DGI).

Not mentioned in the near-incomprehensible internal designation is the engine also has conventional port injection.

Toyota's previous-generation V-6 engines were designated VZ and MZ, the former for rear-drive applications, the latter for front-drive. When a Toyota City team kicked off design and development of the all-new architecture that would become the GR V-6 family, its direction was to replace both predecessors. It would have to power both north-south rear-wheel-drive and east-west front-wheel-drive vehicles, while providing both higher performance and improved fuel efficiency.

The first iteration was 1GR-FE, a 4.0L port-injected V-6 that arrived in 2002 for the 2003 RWD Toyota 4Runner. The following year brought a port-injected 3.0L 3GR-FE for the home-market Lexus GS 300.

A full three years later came a pair of DGI cousins for the RWD Lexus IS 250 and IS 350 sport sedans. For some reason, the smaller 2.5L got the 4GR-FSE designation, while the 306-hp 3.5L dual-injected version was dubbed 2GR-FSE.

Why two injection systems? The conventional 45-psi (3.1 bar) port injection takes care of start-up by itself because it's cleaner and more efficient at doing that, while the high-pressure direct injection operates alone at full load for maximum performance. In between, at most part-load conditions, both operate together (along with the dual VVT-i) to optimize the finely tuned balance of performance, fuel economy and emissions.

Toyota says its unique D-4S dual-injection system is superior to its conventional D-4 port injection because the latter employs a swirl control valve and a high-tumble intake port to achieve a homogenous mixture and stable combustion under part-load conditions. But those nifty tricks also reduce the rate of intake flow. With the D-4S, part-load mixture and combustion are improved by simultaneous injection from both systems without restricting flow.

Direct fuel injection into the combustion chamber offers improvements compared with upstream port injection, including higher compression ratios (enabled by latent heat effects) that provide a thermal efficiency advantage. Toyota says its D-4S further maximizes those benefits because its DGI injectors spray in a wide, double-fan-shape pattern that combines with the port-injected fuel “to provide an ideal mixture.”

“Most engines in North America use a charge motion control valve or high amounts of tumble or swirl in the port to generate a lot of charge motion,” Toyota Technical Center Senior Principle Engineer Dan Yerace says. “So when the fuel is injected, you get blending of the fuel and air for a very good mixture throughout the cylinder that approaches homogeneous.”

Toyota's approach for the 2GR-FSE engine was different.

“To maximize performance, our engineers decided to use the fuel delivery system to provide a homogenous mixture instead of taking the flow losses that you get from putting those mechanisms in the intake manifolds or cylinder heads,” Yerace says.

“By combining direct injection with port injection, and especially by designing the direct injectors to have the proper amount of fuel penetration and dispersion, they could get an even mixture throughout the chamber.”

Even before the later dual-injection versions, this new GR engine family brought new challenges for Toyota's engineers. Because it would have to do double-duty sitting north-south in RWD cars and east-west in FWD cars, one of the most significant concerns was packaging.

Among other issues, that meant the FWD and RWD applications would require different manifolds and exhaust systems.

The VZ V-6s had a cast-iron block vs. the new GR's aluminum block, and the GRs have lower-friction roller-finger-follower valvetrains vs. the previous generations' direct-acting mechanical bucket tappets.

The roller-rockers (as Toyota calls them) “also give you the ability to do lifts a little later and be a little more aggressive with some valve events,” Yerace says. He admits there was a learning curve with the new valvetrain systems, which were fairly new for Toyota, including some oiling challenges.

“You have hydraulic lash adjusters with that system,” he explains, “so the tolerance for oil aeration goes down significantly. If you get air into those lash adjusters, you can have some really bad valvetrain issues, so a lot of things were done to make sure that oil aeration was minimized.”

An upgrade from belts to chain-drive for the camshafts, which helps durability, also required extra attention to minimize noise. Typically, belts, if they are designed and adjusted properly, are a lot more forgiving from a noise, vibration and harshness point of view than chains, Yerace says, so there was a chain development process to minimize the noise.

Another NVH issue typically arises with high-pressure DGI. “Noise definitely is a consideration when you have a high-pressure fuel pump sitting up against the bulkhead on top of your cylinder head cover,” he concedes.

Toyota's first DGI engine hit the Japanese market in 1996, but this latest system did not reach the U.S. for another decade due largely to fear of injector plugging resulting from the inconsistent quality and high sulfur content of gasoline in North America. The door opened when the U.S. and Canadian governments mandated significantly reduced sulfur content similar to levels in Japan and Europe.

Not surprisingly, the cost of this dual system is a bit high, even for an upmarket Lexus. “But when you look at the excellent balance of performance, emissions and fuel economy we can achieve with it, the customers are getting good value for their money,” Yerace says.

And he is quick to point out that among the IS 350's competitors, its 306 horses equal or exceed all but the Infiniti G37, which generates its 330 peak hp at a higher 7,000 rpm. Only the twin-turbocharged BMW 335i offers higher peak torque.

With its standard 6-speed automatic, the IS 350's 18/25 mpg (13-19.4 L/100 km) 2008 EPA economy ratings are among the best in class, and its 5.3-sec. 0-60 mph (97 km/h) performance beats all but the 335i's five seconds flat.

One area where this otherwise delightful V-6 comes up short, however, is its requirement for premium fuel. The 304-hp DI V-6 in the competing Cadillac CTS (also a 2008 Ward's 10 Best Engine) performs quite happily on regular unleaded.

Yerace is coy about the potential of future boosting. “Turbocharging is very, very complimentary to DI,” he says. “I can't tell you what we will or will not do in that area, but we are very aware of the synergies between those two technologies.”

To the question of replacing high-performance V-8s with more fuel-efficient turbocharged DGI V-6s as corporate average fuel economy rules ramp up to 35 mpg (6.7 L/100 km), Yerace says: “It depends on the vehicle platform. There are some really good examples of engine downsizing and some really poor examples. We want to make sure that when people see how Toyota downsizes, they see only examples of how to do it right.”

Ward's 10 Best Engines 2008
http://wardsauto.com/reports/2008/tenbest/10_best_engines_2008

ENGINE SPECS

Toyota Motor Corp.

3.5L DOHC V-6

Displacement (cc): 3,456

Block/head material: aluminum/aluminum

Bore × stroke (mm): 94 × 83

Horsepower (SAE net): 306 @ 6,400 rpm

Torque: 277 lb.-ft. (376 Nm) @ 4,800 rpm

Specific output: 87 hp/L

Compression ratio: 11.8:1

Assembly site: Kamiga, Japan

Application tested: Lexus IS 350

EPA fuel economy, city/highway (mpg): 18/25