From July 1974 both SL and SLC could also be ordered with a fuel-injected 2.8L straight-6 as 280 SL and SLC. US models sold from 1976 through 1979 used the Bosch K Jetronic system, an entirely mechanical fuel injection system. All US models used the 4.5 liter engine, and were called 450 SL/SLC.
In September 1977 the 450 SLC 5.0 joined the line. This was a homologation version of the big coupé, featuring a new all-aluminum five-liter V8, aluminum alloy bonnet and boot-lid, and a black rubber rear spoiler, along with a small front-lip spoiler. The 450SLC 5.0 was produced in order to homologate the SLC for the 1978 World Rally Championship.