By 1968, the muscle car movement was well underway, and Plymouth was a contender with its entry, the Road Runner. The Plymouth GTX was the top-of-the-line muscle car for Plymouth, yet they wanted something cheaper to offer their customers. The two-door coupe and convertible Road Runners could be purchased with the 383ci V8, 440ci V8 , or the Hemi 426ci. The Hemi B-body Road Runner cars have become some of the most collectible because of the 425hp rating as one of the top performers in the Mopar line of engines at the time.