The Camaro and Challenger are both big cars in disguise. The Challenger uses the same platform as a big Chrysler 300. IIRC, the Camaro is built on the same platform as a GTO, considered to be a "big" car. My local Ford dealer had a Shelby and they were asking $80K for it - $13K over sticker price.

Most new muscle cars will run the quarter mile 1-2 seconds faster than similar cars of years ago and get almost twice the gas mileage, with much better exhaust emissions. Adding some headers and a performance tune, will improve the quarter mile times even more. The cars aren't much lighter, but the hp ratings are net, not the inflated gross hp ratings.

My 2014 Corvette gets 20 mpg in town and is supposed to be capable of low 12's. The 455 net hp rating from 376ci is a lot more than a 1970 454ci, 450 gross hp Chevy engine. If I wanted a lot more horsepower, I could install a $5K Procharger supercharger kit, bump the power to 635 and drop the quarter mile time to the low 11's. The Corvette is significantly lighter these days, with the aluminum frame, carbon fiber hood and top. Total cost would be about $68K.

I had a '74 Z28 that only had 240 net hp. It never got better than 12 mpg on the highway and even worse in city driving. I'm sure that it would have been lucky to turn a high 15 quarter mile. The new crop of cars is a huge improvement over that.