First MQB-based car for U.S. is 2015 VW GTI

  • 21-May-2013 07:40 EDT

Volkswagen's 2015 GTI follows sporty-car convention by getting longer, lower, and wider for its seventh generation.

The all-new for 2015 seventh-generation Volkswagen GTI carries a strong enough resemblance to its forebears that it could easily be mistaken for a mildly facelifted version of the current MK VI model.

But the new car sees the GTI follow the Golf base model to VW’s new MQB transverse front-drive architecture, so the familiar-looking sheetmetal clothes all-new underpinnings. The GTI will be the first MQB vehicle sold in the U.S. when it arrives in spring of 2014.

While the increased rigidity and reduced mass of the Golf’s steel chassis are carried over to the GTI, the sport model sees changes to its suspension and turbocharged 2.0-L EA888 four-cylinder engine.

The changes contribute to an 18% improvement in fuel efficiency with the six-speed manual transmission and a 14% improvement with the dual-clutch automatic transmission, according to Volkswagen.

The company estimates that, in typical U.S.-market trim, the GTI has a mass about 55 lb (25 kg) less than the outgoing model. Externally, the GTI is 55 mm (2.2 in) longer and 13 mm (0.5 in) wider, but 27 mm (1.1 in) lower than before. Those dimensions trim frontal area from 0.73 to 0.72 m² (7.9 to 7.8 ft²).

Power up

The EA888 engine is notable for its head design that incorporates the exhaust manifold into the head casting, providing water-cooled exhaust gas recirculation and contributing to faster coolant warmup.

The water-cooled exhaust also means that the engine does not need to use fuel-wasting enrichment to cool the exhaust charge during hard driving, according to engineer Sebastian Willman. That was a significant contributor to the car’s improvement in fuel economy, he said.

The engine uses an IHI Charging Systems turbocharger to pressurize the intake charge at 1.2 bar (17 psi) with a 9.6:1 compression ratio. These figures are lower than we’ve seen with other recent direct-injected engines, but with standard output of 217 hp (162 kW) and 350 N·m (258 lb·ft), the engine delivers impressive results. The turbo is not a twin-scroll unit, but it does pair the cylinders to match 1 with 4 and 2 with 3 to avoid mismatched pulses in the exhaust interfering with other cylinders, said Willman.

An optional Performance Pack tweaks the engine’s software to add 10 hp (7 kW) for a total of 227 hp (169 kW). Changes to cam, ignition, and fuel timing boosts output at peak rpm, but does not affect torque.

The GTI’s engine features variable cam timing, with 60 degrees of range on the intake cam and 30 degrees on the exhaust cam. It also has a two-stage variable lift on the intake valves. Exhaust valve lift is fixed because the benefit of variable exhaust valve lift is too small to justify the additional complexity and expense of the hardware, Willman explained.

With the standard engine, the GTI accelerates to 100 km/h (62 mph) in 6.5 s and reaches a top speed of 246 km/h (153 mph). The optional performance pack shaves a tenth of a second from the acceleration time and adds 4 km/h (2.5 mph) to the car’s top speed.

Handling upgrades

Another part of the performance pack is a computer-controlled Haldex locking differential. It works along with other new features such as a variable-ratio steering rack and XDS dynamic stability control software to sharpen the GTI’s reflexes and minimize the common challenges of front-drive sporty cars.

The variable steering rack reduces the lock-to-lock range for the GTI to 380° from the base Golf’s 500° of motion, for quicker response. The variable spacing of gears on the steering rack prevent it from being too abrupt at steering wheel angle extremes.

The electronic stability control software has been massaged for a delayed intervention that engages less intrusively. The XDS system, as it does on the outgoing GTI, also reduces the need for steering input by helping shepherd the GTI through turns with the application of inside rear brakes to help rotate the car.

The computer monitors wheel speed, vehicle speed, yaw rate, and lateral acceleration to judge when to apply the locking differential. It uses a multi-plate clutch unit that connects the right halfshaft with the differential case, with locking pressure applied proportionally by an electric motor-driven pump that is controlled by the computer in consideration of the various inputs.

The device applies a maximum locking moment of as much as 1600 N·m (1180 lb·ft) to direct torque to the wheel with more available grip. All power can even go to a single wheel in extreme situations, but cornering performance in sporty driving is assisted by the system’s ability to shift torque to the outside front wheel in turns to minimize understeer.

This proactively assists the car rather than reactively helping with the application of brake pressure, points out John Barlage, Director of Global Product Strategy for BorgWarner TorqTransfer Systems. “[Stability control systems] typically come on after the fact,” he said. “We actually interlink the two wheels together.”

An advantage over limited slip differentials, which are popular equipment on other sporty models like the GTI, is that the amount of slip they allow is fixed, based on the engineers’ best guess of what will be most beneficial most of the time. In contrast, having the computer automatically lock and unlock the Haldex differential in response to conditions in real time gives an optimized result, Barlage said.

Another advantage of the system is the ability to lock the inside wheel under deceleration, to invoke some understeer to offset the common phenomenon of lift-throttle oversteer in front-drive cars, he added. Haldex is showing the locking differential to other OEMs, so it may proliferate beyond the GTI in coming years.

More conventional handling aids include a new tubular front anti-roll bar that has its rubber bushings directly vulcanized to the bar in a bid to eliminate any potential noise from the bar rattling inside its bushings.

Electronic aids

The GTI features a raft of the latest infotainment and safety electronics, such as adaptive cruise control, forward collision warning with emergency braking, post-collision braking, lane-keeping assist, driver alert, and park assist systems. A DynAudio sound system is standard in world markets, while U.S. cars receive Fender-branded auto systems.

GTIs for global markets are made at Volkswagen’s Wolfsburg plant, while North American GTIs will come from the company’s Puebla, Mexico, plant starting early in 2014.

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