AFAIK, Twin Spark on BMW twins began in the 2004 model year. Bottom line, what is Twin Spark? In the airhead days (and Harley twins, too), dual ignition meant 2 spark plugs per cylinder. Local dealership tells me that BMW Twin Spark means the plug fires on both the compression and exhaust stroke. This suggests to me an emissions benefit rather than a performance benefit. What's the real deal?