I've been reading up on Aston's involvement with GT racing and I'd like to learn more. Anyone know of a good reference that summarizes the primary regulations that define which cars can compete within each class (GT1, GT2, GT3, GT4)? I'm talking about things like horsepower, weight, and other critical car specs. I've searched the interwebs for this information with my google machine, but I just seem to get a lot of garbage. Thanks!