I have always assumed the BMW vehicle naming conventions represented the engine size, e.g. a BMW 118d suggests it's a 1 series model with a 1.8 litre diesel engine and similarly a 320i suggests it's a 3 series model with a 2.0 litre petrol engine.
But then they throw a 123d into the mix and the pattern doesn't quite follow. What does the 123 mean? Is it related to BHP? Twin turbo?
Can anyone shed some light onto this or provide a list of engine sizes and their meanings?