system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are certain BMW engines (E30, E46, etc.) special to drivers and gearheads?

I don't really think about how engines differ besides cylinders and horsepower.  So what is it about BMW engines made a couple decades ago that sets them apart from other cars and even newer editions of BMWs?
gpt
The designations you listed are for the chassis. The E30 is the 3 series from the 80s, and the E46 is the 3 from the early 2000s. The E30 had the M20 inline 6, or in M3 form it had the S14 4 cylinder. The E46 had variations of the M54 or S54 inline 6 engines. They have different characteristics but they're all fun engines in their own way.

I currently own a 2001 330I with the M54 engine and a 2011 Z4 with the N54. The M54 is a silky smooth engine that progressively builds power nicely. It purrs at idle, hums nicely at cruise, and roars at full throttle. The N54 is a totally different beast. It's got a coarser idle, and with its twin turbos it develops loads of power very quickly off idle and holds it to high rpm.

The S designated engines in M cars until recently were all non turbo engine that were developed for instant response. Individual throttle bodies and aggressive cams meant they'd give you the power your right foot asked for almost before your foot moved. They tend to develop their power at very high rpm so you had to keep the engine spinning fast to get the most out of them.

Pretty much all of them have a fun character. Many modern cars make okay power, but they sound harsh or just don't seem like they want to rev. Others will rev forever but make crap for power down low.