In 1978, Porsche introduced the new version of the 911, called the 911SC (Super Carrera). It featured a 3.0 liter engine with Bosch K-Jetronic fuel injection and a 5-speed 915 transmission. Porsche broke away from using magnesium crankcases like in the late 2.0, 2.2, 2.4, and 2.7 liter engines. This was the start of what are considered by collectors to be the most reliable 911s.
Source: Wikipedia, 2011