BMW M78

BMW M78
Overview
Production	1933–1950
Layout
Configuration	Straight-six engine
Displacement	1.2 L (1,182 cc) 1.5 L (1,490 cc) 1.9 L (1,911 cc) 2.0 L (1,971 cc)
Cylinder bore	56 mm (2.20 in) 58 mm (2.28 in) 65 mm (2.56 in) 66 mm (2.60 in)
Piston stroke	80 mm (3.15 in) 94 mm (3.70 in) 96 mm (3.78 in)
Cylinder block material	Iron
Cylinder head material	reverse-flow, iron
Valvetrain	OHV
Valvetrain drive system	chain
Combustion
Operating principle	spark ignition (Otto)
Fuel system	2 × horizontal draught carburettor
Fuel type	Petrol
Chronology
Predecessor	None
Successor	BMW M337

The BMW M78 is a petrol overhead valve straight-six engine which was produced from 1933 to 1950.^[1] It is the first straight-6 automobile engine produced by BMW, an engine layout which has been a key feature of the brand for many years since.^[2]

The M78 was launched in the 1933 BMW 303.^[3] In 1936, the higher performance BMW M328 straight-six engine began to be produced alongside the M78. In 1952, the BMW M337 engine was introduced as the replacement to the M78. Compared with the M78, the M337 has a revised cylinder head, a new inlet manifold and a reinforced crankshaft with bigger, more modern bearings.^{[4]: 88 [5]}