As Ford transitioned to metric engine displacement designations at the end of the 1970s, the standard engine for the Marquis was now a 4.9L V8 (rounded up to 5.0L, to distinguish it from the 4.9L I6); the rebranded 302 V8 was shared with the Cougar, Monarch, and Zephyr. A 5.8L V8 (the 351 from the Cougar XR7) was offered as an option. For 1980, a 4.2L V8 (a smaller-bore version of the 4.9L engine) became the standard engine on base-trim versions of the Marquis, with the 5.0L V8 shifting to the Brougham and Grand Marquis.