Terry, you're right about the modern cars being heavier than the old muscle cars, which is one more reason by the gap in stock to stock performance shouldn't be as great as it is. Several years ago I was at a car show in Aptos, just south of Santa Cruz, and a couple was there with their two Challengers. They were both painted that purple MOPAR color (IIRC it was called Goofy Grape). His was a '70 model and hers was a current model. I had always thought the new ones looked like the old ones, but the '70 was a lot lower, a lot wider and just generally better looking. The new one looked like a Detroit sedan parked next to it. Still, I would bet that the big mama would clobber the '70 head to head. Beyond tires there is also the issue of computerized ignitions and fuel injection.