I love to read these oil discussions-I really don't think Harly tests anything but their oils and -That said, if Syn 3 works just fine, think how much better Red line and amsoil will work in your Bike. I have also wondered why Amsoil wouldn't test their oil against Red line and went to the source-The amsoil tech line- They told me that Redline was a good oil, BUT they didn't see any reason to test against them because they were such a small company. I use Amsoil racing 20w50 in the engine, 10w40 in the primary,%[email protected] and severe gear in the tranny and change them every 5000 miles-I 'm sure Red line oil would work just as well-Al