Porsche Cranks Up Engine Power With Direct Injection

DETROIT – After skipping a model year, Porsche AG’s Cayenne cross/utility vehicle roars back for ’08 with freshly revised powerplants sporting the hottest new technology for gasoline engines: direct injection.

Direct-injection gasoline (DIG) fueling and increased displacement for the luxury CUV’s DOHC V-6 and V-8 engines means Porsche is able to inject the ’08 Cayenne with meaningful boosts of power while simultaneously reducing fuel consumption, Wolfgang Durheimer, Porsche’s executive vice president-research and development, says.

Durheimer tells Ward’s at the North American International Auto Show here that despite power improvements of as much as 17% in the case of the 3.6L DOHC V-6, the more powerful Cayenne engines deliver an average of 8% better fuel economy, based on new European Union driving cycles.

Porsche’s testing, on its own driving cycle that includes high-speed Autobahn cruising, has demonstrated gains nearing 15%.

“Fifteen percent (fuel economy improvement), from our point of view, will be what the typical customer will experience,” Durheimer says.

A Porsche spokesman says the new Cayenne Turbo – with a 4.8L DOHC V-8 flaunting no less than 500 hp and 516 lb.-ft. (700 Nm) of torque, vs. the 450 hp and 460 lb.-ft. (624 Nm) from the superceded 4.5L V-8 – will get 13 mpg (18 L/100 km) in city driving and 20 mpg (11.8 L/100 km) on the highway.

Porsche increases power, efficiency of '08 Cayenne engines.

This compares favorably with the smaller and considerably less-powerful outgoing turbocharged V-8.

But Porsche customers likely don’t choose the brand for fuel economy, so the primary goal in adding engine displacement and DIG fueling is to improve performance.

In addition to the Cayenne Turbo’s horsepower and torque gains, the Cayenne S’s normally aspirated 4.8L DOHC V-8 jumps from 340 hp and 310 lb.-ft. (420 Nm) of torque to 385 hp and 369 lb.-ft. (500 Nm).

The largest gain, however, is for the Cayenne V-6, which goes from 247 hp and 229 lb.-ft. (310 Nm) for the outgoing 3.2L unit to 290 hp and 273 lb.-ft. (370 Nm) for the new 3.6L V-6.

Durheimer says the improved engine performance is attributable to increased displacement and DIG fueling, which enables higher compression ratios.

The V-6 moves from an already impressive 11.5:1 compression ratio to 12.3:1. The V-8 is boosted from 11.5:1 to 12.5:1, and the turbocharged V-8 has a compression ratio of 10.5:1, up from 9.5:1.

Durheimer says the V-6, in particular, has been heavily revised. The unique “narrow-angle” vee design, pioneered by the Volkswagen Group, goes even further, reducing the vee angle from 15 degrees to just 10.6 degrees.

Durheimer will not confirm whether Porsche is planning to adapt its DIG fueling for its signature “boxer” horizontally opposed 6-cyl. engines that powers its 911 and Boxster/Cayman sports cars – but he does say “the technology is going to be applied to other Porsche engines in the future.”

He adds the ’08 Cayenne model range also enjoys aerodynamic enhancements that also contribute to improved fuel economy. The Cayenne’s coefficient of drag has improved from 0.38 for the V-6 and 0.39 for the Cayenne S and Turbo to 0.35 for the new models.

“A lot of aerodynamic work went into the new Cayenne,” Durheimer says, adding the new models include Porsche Dynamic Chassis Control, a hydraulically actuated system that stiffens the anti-roll bar links to reduce body roll.

At cornering forces up to 0.65 g, the system keeps the Cayenne body “perfectly flat.” This he says, enhances occupant comfort and security. The system also improves safety, by allowing more of the tires’ contact patch to stay on the tarmac.

Porsche says the worldwide breakdown for Cayenne sales is approximately 35% Cayenne (V-6), 45% Cayenne S (normally aspirated V-8) and 20% Cayenne Turbo.

The ’08 Cayenne model range goes on sale in the U.S. in the first week of March.

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