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.