Chrysler's small-block family of engines, known as the "LA" series, has a long and celebrated history in many of the Mopar muscle cars of the 1960s and '70s, and in other vehicles. Although the family can be considered to include the succeeding Magnum series, as well as six- and 10-cylinder derivatives, it was prevalent in the original series of V-8s, consisting of the 273, 318, 340 and 360. Each is named for its displacement in cubic inches. In metric terms, the engines displace between 4.5 and 5.9 litres.
The 273 was the first of the LA engines. Introduced in 1964, it was used through 1969 in Dodge Darts, Plymouth Valiants and other vehicles. The standard two-barrel 273 had a compression ratio of 8.8 to 1 from 1964 to 1966, and 8.6 to 1 for '67 through '69; it used N14Y spark plugs. The four-barrel, high-performance version of the 273, introduced in 1966, used a 10.5-to-1 ratio and N10 plugs. The spark plug gap is .035 inch; distributor point gap is .017 inch. Distributor dwell angle should be between 28 and 32 degrees. Idle speed specifications for the 273 range between 500 and 750rpm depending on model year and transmission.
The 318 was introduced in 1967. Early editions use N13Y spark plugs, while 1976 and later engines use RN12Ys. The compression ratio was 9.2 to 1 until 1972, when it dropped to 8.6 to 1. Distributor point gap is .017 inch. The dwell angle must be between 30 and 34 degrees. For 1972 and 1974, ignition timing is top dead centre (TDC), as it is for '73 except for cars with manual transmission, which should be set to 2.5 degrees before top dead centre (BTDC). For '75 and '76, ignition timing is 2 degrees BTDC. For '77 it is 8 degrees BTDC. For '78 two-barrels and all '79s, ignition timing should be set to 16 degrees BTDC, while for '78 four-barrels should be set to 10 degrees BTDC. The correct idle speed ranges between 500 and 700rpm from 1967 through 1969, and between 700 and 750rpm from 1970 onward.
The 340 debuted for 1968 as a high-performance engine but ran only through the 1973 model year. It uses N9Y spark plugs, with a gap of .035 inch. The compression ratio is 10.5 to 1 for most years, 8.5 to 1 for 1972 to 1973. Distributor point gap is .017 inch. Dwell angle should be between 30 and 34 degrees. For 1972, ignition timing is 2.5 degrees BTDC for cars equipped with an automatic and California cars, and TDC for non-California cars equipped with a manual. For 1973, ignition timing is 5 degrees BTDC for manually shifted cars and 2.5 degrees BTDC for automatics. Correct idle speed for 1968 engines is 700rpm for manual-transmission cars, 650 for automatics. For 1969, it is 750 for manuals and 700 for automatics. For 1970, the corresponding figures are 950 and 900rpm for the four-barrel-carburetted engine, and 1,000 and 950rpm with the special "Six-Pack" engine featuring triple two-barrel carbs. For '71, the correct idle speed is 900rpm. For '72 and '73, it is 900rpm with manual transmission and 750rpm with automatic.
The 360 was introduced in 1971 and continued through 2002. Engines through 1973 use N9Y spark plugs; '74-'75 engines use N12Ys; '76 and later use RN12Ys. Spark plug gap is .035 inch. The compression ratio is 8.7 to 1 for 1971 engines, 8.8 to 1 for 1972 and 8.4 to 1 beginning in 1973. The 360 uses an electronic distributor. Ignition timing for the 1973 engine is 5 degrees BTDC with manual transmission, 2.5 degrees BTDC with automatic. For 1974, the timing changes to -15 degrees Cor the automatic and -16.4 degrees Cor California manuals, while remaining -16.4 degrees Cor other cars equipped with a manual. For '75 and '76, ignition timing is 2 degrees BTDC, while for '77 it is 10 degrees BTDC. For '78 it is 20 degrees BTDC except for the four-barrel engine, which uses 16 degrees BTDC. For 1979 all 360s use 16 degrees BTDC. The 1973 engines use 750rpm as the hot idle speed. For '74 and '76 engines, 850rpm is the correct speed. For '75 it is 750, or 850 for the four-barrel outside of California. For '77 it is 700, while for '78 and '79 it is 750.