E stands for Entwicklung or "development" and refers to a body style, not an
engine.  Your '06 325 is an E90.

http://www.turnermotorsport.com/html/e_code.shtml

Tom K.

Your CAR is an E90, this is the chassis code or model designation. Therer
are many different versions of the 3 Series cars, mine is the E36, the E46
is the model that followed, and yours is the E90.

The ENGINE code is different. My engine is the M50, my chassis also gets the
M52 as the two 6 cylinder offerings. The M cars get the S50 and S52, and the
4 bangers get the M42 and M44. I'm not certain which motor you get, but my
instinct is that it shoujld be the M52.