I think you're talking about the N54 correct? That was the older twin-turbo engine. It was super mod friendly (minor mods pushing 400+ hp), but there were tons of issues, such as injector problems, carbon build-up, turbos needing replacement, and above all, the HPFP used to grenade. BMW did step up to the plate and warrantied everything up to 100k miles (don't remember the exact coverage)
The replacement was the N55, which produced the same power, but is a twin-scroll single turbo. It wasn't as mod friendly, but they solved most, if not all, the problems with it. They're practically bulletproof now. The only issue that can crop up with the N55 nowadays is the HPFPs (rare though), but that's a pretty easy fix. BMW covers them and a dealer can do the replacement within a few hours.
For MY16, they're finally dropping the N55 and bringing out the 340i with new B58 engine.
That being said, I've driven so many N54/55 cars and prefer the N55. There is no turbo-lag with the N55 and I wouldn't be scared to own one out of warranty, but the N54? No thanks, even if BMW is footing the bill. Not worth the headache. I'd find a 1 series with the N55.
The N55 is the reason why BMW is one of the leaders in forced induction now.
Ah, that's exactly what I was wondering. Model year 2011 started using the N55 and that's what I will look for then. Thanks!