A classic Porsche 911 engine has six cylinders.
The 911 is defined by its rear-mounted, horizontally opposed flat-six engine. Porsche introduced the model in 1964 as a larger and more powerful successor to the four-cylinder 356, using a 2.0-liter air-cooled boxer-six in the earliest production cars. In a flat engine, the cylinders extend horizontally from opposite sides of the crankshaft rather than standing in a V or vertical bank.
Air cooling was a signature of early 911s, continuing through the 993 generation. Porsche switched regular production 911s to water cooling with the 996 series in 1998, but retained the six-cylinder boxer layout. Modern 911 variants continue to use flat-six engines, including turbocharged versions and naturally aspirated performance models.
The wording “classic” can cause confusion because Porsche also made related models with other engine layouts. The Porsche 912, for example, used a flat-four, while some Porsche racing cars used flat-eight or other configurations. Those exceptions are not the standard 911 engine, whose canonical answer is six cylinders.