lol..my friend just put a new Corsa exhaust on his Vette. The guys there use Amsoil. I told him that I would use Mobil 1 0w-40 but he told me how Chevy specifically states not too use a 40wt oil. I called up the Mobil tech line (what joke they are) and spoke to someone decent this time. He said "..in Europe they care more about protection, but in the US we have all of these **** tree huggers around so it's about emissions and mpg." Heard it from the horses mouth. His buddies by the way, run M1 15w-50 when racing Z06's. When looking at the product data sheets you will also find it says you can use a 50wt or 40wt where ever a 20wt,30wt or 40wt is called for. So it doesn't matter. Just thought I'd share this wonderfull information.