Porsche Cayenne S Hybrid - Click above for high-res gallery

While charging along at 85 mph with a particularly poker-faced Porsche engineer riding shotgun, traffic begins to cluster on the horizon. Not willing to risk our seven-figure prototype, I gently roll off the accelerator, at which point a funny thing happens: Without warning, the tachometer needle dies, unceremoniously plunging to zero RPM. The supercharged, 3.0-liter V6 ahead of us has gone stone dead, yet our Porsche Cayenne continues to waft along unruffled. We are coasting along on the Autobahn, with only a modest bit of wind noise and tire roar as our soundtrack.

Just as quickly as it began to appear, Stuttgart's traffic thins, and after gliding along for perhaps 15 or 20 seconds -- losing remarkably little velocity -- I ease back onto the throttle, at which point the rev counter jumps back to life just as quickly as it had extinguished, and the Cayenne sashays back up to 95 mph before I slot in amongst slower traffic in the right lane. Beyond the tachometer's telltale drop and jump, there is exactly no indication that the engine momentarily packed it up just seconds before. My copilot, Dr. Michael Leiters, project manager for Porsche's Cayenne Hybrid, allows himself a brief smile.

Far from indicating a mechanical defect, we've just witnessed what our Deutsche companion refers to as "segeln" -- sailing -- a fuel saving maneuver that Porsche says other automakers have written off as impossible at roadway speeds without jolting disruptions. Yet beyond the tach needle's machinations, there has been no drama whatsoever: no untoward thwack in the back, no expensive-sounding noises, no head toss, no coffee spilled, just seamlessly reintroduced acceleration. The gas pedal simply called upon the engine again and the electric motor restarted it in a flawless, 300-millisecond passing of the power baton. Remarkable stuff.

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Our travel and lodging for this media event was provided by the manufacturer.

Porsche Comes Through In The Clutch

Unlike any other gas-electric system currently on the market, our Cayenne S Hybrid tester has an additional mechanical clutch that decouples the engine entirely, temporarily removing it from the driveline equation. Doing so means the V6 is not a source of parasitic drag, and the modestly-sized 52-hp electric motor can nudge the Cayenne gently along as it does its inertial thing unencumbered. What is "modestly-sized," exactly? Porsche says the complete hybrid module – including the electric motor and the additional clutch – is just 5.8-inches long.

The German automaker figures this electronically-orchestrated party trick will save them a couple of percentage points when it comes to fuel consumption, but we reckon that the gains could be substantially greater under the right conditions – a drive route incorporating long downhill grades, say. If one lives in a mountainous area like Denver, Colorado, it's theoretically possible to start the Cayenne's ball rolling, and then coast all the way down to the base of a slope – a run that can sometimes last for many miles – without using a drop of fuel and without resorting to tactics like shifting into neutral to avoid engine braking.

In fact, using the brakes to slow one's descent will store energy in the nickel-metal hydride battery pack thanks to regenerative braking technology, so theoretically the entire descent could result in a net-energy gain. If you're particularly delicate with the throttle, this sub-cargo-floor mounted battery pack should allow for slow-speed electric-only running for up to 1.2 miles, but in practice we found this harder to do than with other gas-electric systems we've experienced.

Porsche's so-called "Hybrid Manager" is no small achievement – this bit of hardware supervises all major systems (engine, electric motor, transmission, battery, etc.), and reacts by issuing any of 20,000 data instructions, as compared to a traditional ECU that requires only 6,000 commands. Porsche notes that the 'sailing' capability can be activated at speeds of up to 86 mph (far faster than that of other hybrid systems), making it a viable energy-saving partner for both city and highway duties.

Gearing Up

Unlike most hybrids, Porsche says the production hybrid Cayenne will eschew use of a continuously-variable transmission unit in favor of a more conventional eight-speed gearbox from Japanese supplier Aisin, albeit one with an electrically-driven oil pump. Why no CVT? Officials explain that while this Cayenne is a hybrid, it is first and foremost a Porsche, and CVTs generally fail to deliver the sort of driving enjoyment that a conventional Tiptronic can. Despite their many advancements over the past few years (including the institution of paddleshifters with artificially preset ratios to preserve the mental "shifting" experience), we agree wholeheartedly.

Our tester's powertrain suffers no "stretched rubberband" moments that are the hallmark of most CVTs, and it was all the better for it. Unusually, top speed is reached in sixth, with the seventh and eighth cogs reserved as fuel-savers. It's that top gear that allows the Cayenne to "sail" at 86 mph with the engine shut off and the electric motor coaxing it along. We inquired as to the viability of a dual-clutch transmission like the PDK, but were told that fitting one would be tremendously difficult, so for now, Tiptronic it is.

In nearly every other area of operation, our prototype parallel hybrid functions in an almost indistinguishable manner versus a traditional gasoline-powered Cayenne. The combustion engine has been borrowed from Audi, with a belt-driven Roots-type supercharger nestled between its directly injected cylinders. So equipped, the engine generates 333 hp and 324 pound-feet of torque. Unlike in other gas-only Audi applications, the air-conditioning compressor and electrohydraulic steering pump are powered by the battery pack. For its part, the electric motor adds up to 221 pound-feet of torque. Combined, Porsche figures the two power sources are good for 374 bhp and 405 lb-ft of torque at just 1,500 rpm.

As part of its energy-saving regimen, the hybrid will be the first Cayenne to utilize electrohydraulic power steering. Porsche says it consumes 93% less energy than its conventional hydraulic counterpart, and in our limited drive time, it managed to deliver good accuracy, although we wouldn't mind it if Porsche dialed in a skosh more weight at highway speeds.

By The Numbers

While final fuel economy testing has yet to be completed, Porsche expects the powertrain to deliver performance akin to that of the V8 Cayenne while sipping fuel like a four-cylinder. 0-62 mph checks in at a conservatively-estimated 6.8 seconds, and top speed is limited to 133 mph. Even towing capacity and off-road ability is said to be unchanged. What is different, however, is miles-per-gallon and C02 output -- the latter figure being of great importance to those living under the various Byzantine emissions-based tax structures that govern most European nations. Porsche's new hybrid drivetrain sips fuel to the tune of 8.9 liters of fuel per 100 kilometers (62 miles) traveled when measured on the New European Driving Cycle (around 26 mpg U.S.), equal to C02 emissions of less than 210 grams-per-kilometer. That's an improvement of more than 25% over the V6 Cayenne, and the production vehicle is expected to be ULEV II compliant when it comes to North America.

While other automakers have elected to play up their vehicle's hybrid credentials, it is likely that Porsche will choose a more restrained route when the Cayenne Hybrid reaches production. The massive hybrid decals that run along the bottom of the bodysides won't be a mandatory "feature" as they are on General Motors' GMT900 SUV hybrids, and Stuttgart has not yet determined how it will badge the vehicle. Inside, Porsche has also resisted going the "Greener Than Thou" route with lots of fancy fonts and gimmicky display graphics like wilting digital flower petals. No games. No "monkey cinema" as Dr. Leiters refers to it. Oh, there's a screen that can be summoned on the navigation system which details where energy is being routed and a small in-cluster indicator, but Porsche assumes that you'll ignore these after you get used to hybrid driving. In stereotypically Germanic fashion, this Cayenne is all business.

Why Not The Diesel?

Despite much purist hand-wringing upon its introduction, the Cayenne has been the linchpin in Porsche's product portfolio since going on sale in 2002, particularly in the States. And although officials aren't talking model-mix projections, this gas-electric model figures to be an especially important offering in hybrid-happy America. For the moment, Porsche says it has no plans to bring over its excellent new Cayenne diesel, a powertrain whose great slugs of torque and excellent highway fuel economy is perhaps better suited to typical U.S. driving patterns (hybrids are most effective when poking along in thick urban traffic, where slow-speed trundling from bottleneck-to-bottleneck can often be conducted purely on electric power, but fewer Americans live in and around major city centers compared to their European counterparts). Despite this, America's appetite for diesels is still dwarfed by that of Europe, and with inflated fuel prices (versus gasoline) and soot-spewing memories of diesels past, it is likely that Rudolph Diesel's combustion cocktail will remain second fiddle to hybrids for some time.

Pricing also figures to be something of a sticky wicket, as all of the requisite hybrid R&D and associated hardware figures to add something on the order of $15,000 per unit (Porsche will not disclose projected sales volumes). That's a premium far too great for customers to absorb – even with the possibility of tax breaks. In light of this cost barrier, we expect for the Cayenne hybrid to sticker for something well north of a conventional V8 S model, ($60,215), perhaps along the lines of $67-70k, albeit with additional standard equipment to soften the blow. Given that performance is similar to the V8 engine and that fuel economy and emissions are markedly superior, this figures to be a reasonable surcharge for affluent folks eager to play the "green card."

What's Missing?

Porsche says that their hybrid system is "only about 90% of the way there," although at first blush, it's already so polished that we struggle to think where a 10% improvement could come from. If we have any reservations with this setup, it's a sin by omission -– a lack of noise. The inherently quiet nature of a parallel hybrid ignores the important aural performance link that Porsche has worked hard to establish with its vehicles and with the Cayenne in particular. Remember the commercial with the new owner revving his Cayenne Turbo in his driveway? How about the more recent and altogether fabulous Cayenne GTS "bloodlines" spot? While the 3.0-liter V6 in the Cayenne Hybrid S is a very good engine, it isn't terribly special sounding, and at points it makes no noise at all. What's more, we suspect that the consternation surrounding the pedestrian safety risks associated with silent-running hybrids and electrics will only grow when more vehicles reach elevated speeds.

While we could go on about other key aspects of this Cayenne – the handling, ride and interior -- our drive was limited in time and scope, meaning that beyond concentrating on the hybrid powertrain, we didn't have much time to assess the total driving experience. Not that this is a real problem, as it's all likely to change appreciably the time the Cayenne Hybrid comes to market.

How's that? Although officials would say little that wasn't non-committal, we know that the next-generation Cayenne is well along in development, and it is poised for release sometime after the Panamera launches, likely in 2010 as a 2011 model. As Porsche is smart enough not to bother with the expense of fitting and certifying a brand-new drivetrain for a vehicle that's about to go off the market, we can reasonably surmise that the hybrid hardware we sampled will arrive underneath new sheetmetal, bringing with it a different driving experience.

Making Sense Out Of A Topsy-Turvy World

If nothing else, our stint with the Cayenne Hybrid S served to reinforce that we live in interesting times. General Motors, once the world's largest automotive power, is on the brink of bankruptcy. Hyundai, a Korean company, are the orchestrators of this year's reigning North American Car of the Year – a rear-drive luxury sedan, no less. And we've just driven an electrified Porsche truck whose raison d'être is better fuel economy and lower emissions.

Say what you will about Porsche bringing the Cayenne to market in the first place, but having driven damn near every derivation of the vehicle ever sold in the States, this author can say it remains a startlingly omniscient piece of machinery capable of just about anything -– and now, a remarkably green performance. While the looks of the Cayenne and its button-crammed interior have yet to grow on us, its performance on the street and on Porsche's balance sheet has proven to be nothing to sneeze at. The model line's 250,000 unit sales history has given Porsche the development dollars to continue advancing enthusiast-oriented models like the 911 and Boxster, while allowing it to become one of the world's most profitable and powerful automakers. If Porsche has to add a little green to its otherwise blue blood to keep churning out 911 GT2s and Cayman S coupes, so be it – the Cayenne Hybrid S has a lot to recommend it.

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