OK, so I know the "x" in the badge designates an all wheel drive vehicle, but other than that can someone list out what all of the various letters in the BMW badge translate too (both current and old)? I am often confused about what I am looking at when following the various versions of 330 or 328 somethings on the road.

BMW naming convention

BMW's numbering system is fairly simple. Numbers, usually odd numbers, indicate the relative size and expense of cars. Everyone has heard of BMW's 3-series, 5-series and 7 series cars. In Europe, BMW sells the bargain-priced 1-series.
The next two digits indicate engine size. The BMW 325i has a 2.5 liter engine. The BMW 330i has a 3.0 liter engine.

The letter i is a holdover from times when fuel injection was something to brag about rather than something you would find in even run-of-the-mill economy cars. In Europe, where BMW sells diesel-powered cars, one can also see the 325d on the road.

Sometimes two letters appear after the number, as in the 325Ci and 325Xi. The first letter indicates a special type, as with the two-door 325Ci coupe or the all-wheel drive 325Xi.

While this is true as a rule, it's no longer 100% so for post LCI .

For example, the LCI 525d, 530d and 535d all share the same 3.0litre diesel inline 6, with different tuning levels and, in the case of the 535d, two turbos instead of one.

The same applies to the 530i and 535i which are the same engine, the 535i just being a twin turbo.

If I'm not mistaken, they sell the 1-series here in the US now. :whistle:
I've seen a few at work + a convertible on the freeway.

The 1 Series is in the showroom and on sale in at least one Atlanta dealer. In fact several models were on the floor. Looks like nice toy.

Initially I wasn't sold on the 1-series when they first announced plans for US sales, but when I saw it in person it changed my mind. Looks like a very fun car to drive.

What about "t" or using the same letter twice? e.g. tii, tti. Trying to remember what else I have seens.