Specifically, I am considering either the 10W-40 or 15W-40 from Amsoil combined with a dual remote filter on a 1990 BMW 325 that is going to see track use on a roadcourse, as well as street use. For the next few months, it will be a daily driver in MA, then it will primarily be to and from events, and have occasional use during the week. I figured the 10W-40 would be good in this app, but the 15W-40 appeals to me for a few reasons as well. Primarily, because this car has been run on conventional oil and neglected for 130k, I figured the additive package in the diesel oil might be beneficial. I also like the fact that I believe it has an extra dose of corrosion inhibitors and the car will eventually be idle for days at a time. The only drawback I can see is that the 15W-40 is considerably thicker than the 10W-40 when cold, though it still scores pretty well. Can anyone see any drawbacks to using the 15W-40 under "racing" conditions, as that is really the bigggest issue for me? Has anyone that you know of run this oil under similar conditions, or is it way out of it's element and I'm off my rocker? Any input is greatly appreciated. Thanks.