In the '60s and '70s, "muscle car" most often meant a midsize American coupe with a high-performance V-8 and rear-wheel drive, period. But as Detroit performance started making a comeback in the late 1980s, and with V-8s on the decline, carmakers began stretching that definition.
https://www.hagerty.com/media/market-trends/break-the-mold/
https://www.hagerty.com/media/market-trends/break-the-mold/
