Just a random article on the net.
However, a package is more than the sum of its parts. While the Mustang GT500 is down on power, its curb weight tips the scales at 3,845 pounds, a whopping 600 pounds less than the hefty Hellcat. The Camaro ZL1 is comparable with the GT500 at just 3,860 pounds when paired with the manual transmission (4120 pounds with an automatic). The GT500 is capable of accelerating from 0-60 mph in just 3.5 seconds and reach a cosmic top speed of 202 mph. Given the weight advantage of the Shelby and slightly smaller frontal area, we highly doubt the Hellcat Challenger SRT will surpass the Shelby despite the horsepower advantage.
All new challengers are heavier than their mustang counterparts, I believe.