I've been using 5W-50 Castrol Syntec in my SVT since I bought it about a year ago. It's still clean when I drain it every 7,000 miles. I also used the same oil in my 350 Chevy 300+HP motor for years. I put a very abused 80,000 miles on that 350. When it was pulled apart for a rebuild there was no ridge on the cylinders and you could still see the cross-hatch from the honing! We put it back together after seeing similar results on the bearings and it's still running today in a '78 Nova at about 135,000 miles. I understand that fairly recently Castrol has changed their formulation, as has Mobil 1. I'm looking to switch to Amsoil on the next change due in a thousand or so miles. Am I crazy? Probably.
