When you're sitting at a stoplight or stuck in traffic—and you're lucky enough to be behind the wheel of a new 2010 Porsche Panamera or 2011 Porsche Cayenne—you might notice the engine ever so smoothly shut off.
Yes, it's supposed to do that; the feature is called Auto Start Stop. But unless you've driven a hybrid, like the Toyota Prius or Ford Fusion Hybrid, for example, you're probably not very familiar with the idea, or the sensation.
To newbies, it can be a little disconcerting. Will the engine restart quickly enough when you need it? Will the air conditioning and all the accessories work seamlessly? And is the system robust enough to handle potentially hundreds of starts and stops in a particular day? The answer to all those questions is yes.
Big in Japen, sought-after in Europe
In more fuel-economy-minded Europe and Japan, the word is out that start-stop systems can save a lot of fuel in gridlock. There, they've already become quite common, especially in upscale yet fuel-efficient vehicles, with BMW and Mazda among several brands becoming leaders in installation.
While lots of automakers have been talking about start-stop—for years, now—Porsche is the first automaker to widely deploy this green feature in the U.S. in its non-hybrid vehicles—including the high-performance Turbo V-8 variants.
It's tough argument for economics alone, as start-stop doesn't boost the Panamera's EPA fuel economy ratings, but in real-world driving in especially congested stop-and-go conditions or through long series of unsynchronized traffic lights it might reduce fuel consumption (and the emissions from idling) by five percent or more.
The U.S. version of Auto Start Stop on 2010 Panamera models defaults to the 'off' position, and each time you start the sport sedan you need to rearm the feature by pressing the button—something that very few drivers—even if they intend to use the system and save fuel—are going to remember.
2011 models will remember your preference
In the 2011 Panamera that's now already on sale, as well as in the 2011 Porsche Cayenne models, that clunky arrangement changes. Start-stop will now return to its last mode of operation—activated or deactivated—as soon as you start the vehicle, and it will remember multiple modes for different users/keys.
We had the chance to take notes on Auto Start Stop and put it through the paces in both the new Panamera V6 and Cayenne V6. But it's a difficult feature to pin down or explain simply. Sometimes you'll be at a stoplight and the engine will stop; other times in seemingly identical conditions it won't; and sometimes the engine turns off a while after you stop or a while before you take off from the light. According to Porsche, start-stop has a total of 56 variables that affect when start-stop temporarily turns the engine off, and for how long—everything from engine temperature and battery drain to recent driving style.
No matter how abruptly you lift off the brake pedal, the engine starts smoothly, almost without a shudder. How are restarts also so seamless? A Porsche official explained that the start-stop system uses data from the crank position sensor and actually primes the fuel injector for the next cylinder to help assure a quick, smooth start.
This story originally appeared at The Car Connection