In 1966 the 425 horsepower Hemi engine was offered as an option on Plymouth's Belvedere II and Satellite models. (The Hemi had been available in 1964 and 1965, but only as a race engine and was not available to the general public).  In factory form, the “Street Hemi” qualified for A/Stock and AA/Stock drag-racing competition. Richard Petty won both the 1964 Daytona 500 and the 1967 NASCAR championship for Plymouth. This Street Hemi package was offered virtually unchanged in 1967. A new upscale performance model, the "GTX," was introduced in 1967, available standard with a 440 CID performance V8.

The Barracuda received a restyle in 1967—one that was well-received by the public, which almost doubled the sporty car's sales.

For 1968 Plymouth restyled its intermediates with more rounded lines and introduced the "Road Runner." This was marketed as a "bare bones" performance car and aimed directly at the youth market, and was available as a hardtop or coupe only. Identified by special wheels, hood, Road Runner emblems, and the famous cartoon bird sticker on the sides and rear, the Road Runner could only be had with either a high performance 383 CID V-8 or the 426 Hemi engine. Plymouth's GTX model, introduced in 1967, was continued.

In 1968 and 1969 Plymouth added new V8 models of its popular Barracuda, the 340 CID "LA" V8 and the 383 "B" performance engine (prior to '68, the largest Barracuda V8 was the 273 "LA" V8). Even so, by 1969, Barracuda sales dropped back to 1966 levels.

In 1970 the Barracuda was completely restyled, sharing an all-new “E-body” shell with another Chrysler performance compact, the Dodge Challenger. A mid-year introduction of the Barracuda was the "AAR" model  (All-American Racer)  with a 340 CID "Six Pack" to allow Plymouth an entry in the Trans Am Series. The AAR was identified by its bold tape stripes. Less than 2,900 AAR models were built.
 
In 1970 Plymouth's Valiant was revived with new styling as a coupe, and, in base form, it was now called the "Duster" while the upscale form was called the "Gold Duster." Also offered was a high-performance variation, the Duster 340. The 4-door was also restyled and continued to use the Valiant nameplate. 

Plymouth's most awesome newcomer in 1970 was the high-performance "Superbird", which was considered part of the Road Runner Series. With its air-splitting, droop-snout front end, sleek body, and tailfins carrying a stabilizer wing high above the rear deck, the Superbird was capable of over 200 miles per hour in racing trim.

In street form, the four-barrel 440 cubic inch engine with Torqueflite automatic transmission was standard on the Superbird. A six-barrel 440 engine, the 426 Hemi, and four-speed manual transmission were optional. The Superbird accounted for 21 of 38 Chrysler victories on the Grand National circuit. When NASCAR changed its rules in 1971, however, the Superbird's dominance of high-speed ovals was over.

By the end of 1970, Plymouth had completed its makeover from the stodgy family sedans of 1946 to a brand name synonymous with performance and high style. While staying in third place among the Big Three's low-price field, it added tons of excitement during the 1955-1970 period. Without these great engineering changes and performance improvements, it is likely that Plymouth would have become an "orphaned brand" much, much sooner than 2001.