IT WASN’T SUPPOSED to be this way. Tighter carbon-emission standards around the world and higher fuel-economy rules in the U.S. were to mean the end of muscle cars, or at least affordable ones. But, pleasant surprise, cars have actually gotten stronger, quicker, faster. Overall, performance is cheaper, more efficient and reliable than ever. It’s the Golden Age of Horsepower, and the horses are eating diet hay.

Do you like acceleration, Johnny? Dodge will sell you a Challenger SRT Hellcat with 707 hp and an eight-speed transmission,...