BMW's

By looking at label on the rear of the car. Example if you see 320i, it means the car is 3 series with 2.0 engine and is an injector. The same goes for say 525i, etc. The first digit always tels you the series while the last two digits will tell the engine.

thats really good info! i always wondered how they got those numbers..... that'll be useful when im out having fun on the streets :)

The first digit still holds true... but the last 2 digits no longer holds. First digit holds for 1, 3, 5, 6, and 7 series. The newest 328/528 has the 2.0 Litre Inline-4 TwinTurbo engine (except for the 128i, which currently still has the good'ol naturally aspired 3.0L Inline-6 engine; the 335/535/640/740 has the 3.0L Inline-6 TwinTurbo engine; while the 550/650/750 has the newest 4.4L V8 TwinTrubo engine. And last but not least, the only one that still holds true for the last 2 digits is the 760Li, which has a 6.0 Litre, 48-valve, TwinTurbo V12 engine that produces a roaring 535 horses.

Once you have the basics, you will have to get into body code referencing. E's and F's all around. Have fun!

like said above, you can tell by the name on the back... usually you can tell by size... the 7 series is obvi, and i guess you could get the 5 and 3 series mixed up because they're similar in size but the styling queues distinct them as well.