The BMW M30 is a SOHC straight-six petrol engine which was produced from 1968 to 1995. With a production run of 27 years, it is BMW's longest produced engine and was used in many car models. The first models to use the M30 engine were the BMW 2500 and 2800 sedans. The initial M30 models were produced in displacements of and . Larger displacement versions were introduced over time, with the largest version being , which was sometimes badged as "3.5 litres". As per the BMW M10 four-cylinder engine from which the M30 was developed, the M30 has an iron block, an aluminium head and an overhead camshaft with two valves per cylinder. The engine was given the nicknames of 'Big Six' and 'Senior Six', following the introduction of the smaller BMW M20 straight-six engine in the late 1970s. The M30 was produced alongside the M20 throughout the M20's production, and prior to the introduction of the BMW M70 V12 engine in 1987, the M30 was BMW's most powerful and largest regular production engine. Following the introduction of the BMW M50 engine in 1990, the M30 began to be phased out. Ward's have rated the M30 as one of the "Top Engines of the 20th Century". Design The M30 was originally developed in the late 1960s, loosely based on the BMW M10 four-cylinder engine first used in the BMW New Class sedans and coupes. Initially, the engine code was "M06" and the "M68", until all versions began to use the "M30" prefix in 1981. Common features between the M10 and M30 include a profile lowering 30-degree slant to the right, a crossflow cylinder head (a gas flow head in later designs) and chain-driven camshaft with rocker arm valve actuation. Further similarities include a cast-iron block with an aluminium head and a forged crankshaft. The first two M30 engines introduced were the and the versions, which both used an bore. M30B35LE/M90 engine The M30B35LE engine, also called the M90, was used in several models from 1979-1982. It combines the block from the motorsports BMW M88 DOHC engine with the M30's SOHC cylinder head. Versions M30B25V The first version of the M30 was introduced in the 1968 E3 2500. This version uses dual Solex Zenith 35/40 INAT carburettors, has a compression ratio of 9.0:1 and produces in most applications. It has a bore of and a stroke of . The M30B25 has