Installed in my 2007 BMW R1200R. A set of four spark plugs is clearly needed as there are four spark plugs on a bike. After installation, initial start-up and a short drive the next day, they seem to work well. I would even say that everything started easier than usual. Not sure how quieter as the engine already seemed quiet at 32,000 miles. I would recommend them and buy them again in 15-20k miles to replace them. Whether he calls for it or not.
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