The 1972 model was nearly identical to 1971 with a few minor changes. The grille design was cleaned up, and the taillights were changed to match the grille’s new aerodynamic look. Side marker lights changed from the flush-mounted side markers to the surface-mounted units adopted across the entire Chrysler line-up for the 1972 model year. The optional bumper guards for 1972 included a rubber strip surrounding the taillights and a rubber strip below the grille. The big differences came in the cutting back of performance options for the car. The suspension, rear axle ratios (a 3:55 ratio was the tallest available), and most noticeably, the engines changed. The big-block 383 was replaced by a larger-bore (and lower performance) 400 CID version as the standard engine. The small-block 340 CID and the performance version of the 440 CID engine (with a 4-barrel carburetor, performance camshaft, and dual exhausts) were also available, and for the last time, a 4-speed manual transmission could be paired with any of the three engines. All of the engines suffered a drop in compression ratios to allow the use of low-lead/no-lead gas and to meet the first round of emissions regulations. The 280 hp (209 kW) 440 engine was the basis for the Road Runner GTX (the GTX was no longer a separate model) and was available on Road Runners from 1972 to 1974. The 1971-72 Road Runner sheet metal was used by several NASCAR racing teams for their racecars and ran well on the circuit during the 1971-74 seasons. Richard Petty won the championship both in 1971 and 1972 using the Road Runner-based cars, winning 30 races over the two seasons.