Why the initial surprise? The world's best known hybrid -- the Toyota Prius -- also has an electric-only mode, but the car has no tachometer. Honda's IMA hybrid system, fitted to vehicles like the Insight and CR-Z, has a tach, but when in cruise mode, the engine never cuts out, so it doesn't make such radical fluctuations. This M Hybrid is the first car we've driven where the tach hibernates every so often.

It also happens to be Nissan's first hybrid of the 21st century. Nissan launched the Tino hybrid in 1999, following Toyota into the hybrid era. But while it did employ a lithium-ion battery pack, putting the company one step ahead of Toyota back then, its limited edition run of 100 units was just a splash in the ocean and didn't put Nissan on the hybrid map. Later, Nissan borrowed Toyota tech for a hybrid version of its Altima, which was a stopgap measure.

Looking identical to its Infiniti M brother apart from the chrome-coated 18-inch alloys, Infiniti's M Hybrid is a different story. Aiming fairly and squarely at the Mercedes E-Class and the BMW 5 Series, and available in the U.S. from spring 2011, the M hybrid will be the brand's first production hybrid. And while we can say it certainly has a street presence, we can't say it's beautiful. With strong design hints from the macho FX SUV, the M Hybrid seems more ready to bludgeon than beautify its surroundings.

The Infiniti is powered by a version of Nissan's ubiquitous 3.5-liter VQ35HR V-6 and a one-electric-motor, two-clutch parallel hybrid system that Nissan refers to as "intelligent dual clutch control." The system combines a number of clever environmental technologies. Without the use of a traditional torque converter, the high-response electric motor and the V-6 engine are directly connected to an electronic 7-speed transmission with a manual shift mode. It's similar in concept to the Porsche Cayenne Hybrid, although the Infiniti does not use a torque converter. So while the M Hybrid can generate better fuel economy, it will also produce more noticeable shift shock.

Interestingly, Nissan did consider the latest 3.7-liter V-6 as a potential powerplant for the M Hybrid, but in the search for the best combination of power versus fuel economy, the 3.5 liter delivered the best figures.

We push the start button in the ergonomically designed cockpit, surrounded by more than 40 switches. As expected with hybrids these days, there's no sound-only the faint hum of an electric motor under acceleration. With the V-6 pumping out 302 horsepower and 258 pound-feet of torque at 5000 rpm, and the electric motor producing a peak 67 horsepower and 200 pound-feet, the Infiniti delivers prodigious power off the line, rivaling that of a V-8. We clocked its zero-to-60 mph time at 5.5 seconds, quicker than most large V-8 sedans. Generating barrels of torque from 2000 rpm, the M is always in the zone, just waiting for the slightest press of the right pedal. It's nearly as quiet as a Lexus, yet reveals its true colors when called on for instant acceleration as the V-6 lets out a refined, yet sporty, tune.

Making sure our lithium-ion battery pack had enough charge, we were able to cruise up to 60 mph in EV (electric-only) mode, constantly amazed at that tachometer sitting on zero. When the battery gauge fell below half, the engine engaged. But even when cruising in EV mode, all we had to do was flex our right ankle and power was there for the taking.