As the 1970s progressed, Mercury began efforts to improve emissions and fuel economy of its full-size range; following the discontinuation of the Monterey and the introduction of the Grand Marquis, smaller-displacement Ford 335 engines replaced the 460 as the standard engine offering. For 1975, the 402 cubic-inch Ford 400 V8 was introduced (largely as a successor to the 429), with the 351 cubic-inch Ford 351M V8 becoming the standard engine for the Marquis in 1978. In California and for "high-altitude" use, the 400 remained standard equipment; regardless of usage, the 460 (standard on the Marquis Brougham and Grand Marquis through 1977) remained available as an option until the end of the generation. The C6 transmission remained paired to the 460, with the 400 and 351M using the lighter-duty FMX transmission.