The standard equipped muscle cars of the late 60s and early 70s came off the shelf as 5 or 6 sec cars, just full of torque and grunt. Then in the late 70s and thru 80s, the US strict emissions laws and oil prices took a toll on these strong engines. The manufacturers had to retard the cam considerably, reduce from 4-barrel cards to just 2-barrel thingy, fitted 2 catalytic convertors, a smaller diameter pipe after the silencer box/muffler, leaner mixtures on wide range of rpm blah, blah, blah ..... all these just killed the genuine bhp. but some manageable torque more or less remained to still push the cars.
So most people then decided (similar to what I did before) to change some critical parts without affecting the overall emissions by using various approaches. I guess there are ways of going behind the law in some states in the US. Simple approaches like breaking off the seal at the 4 barrel carbs & repositioning the float level and retuning to a richer mixture, changing to an advanced cam, ign. retiming, fitting an adaptor plate between the manifold and carb, cutting off the cats, fitting twin exhaust systems etc etc made a whole lot of difference, that many had to get used to the accelerator pedal which has now become very responsive. I personally had that experience and I couldn't control the car at take-off after this simple mods.
