i've driven bimmers with the N54 engine, tune and without.
the N55 picks up very quick, and very smoothly.
for stock, i like it very much...i like it alot!
I personal would like it a little more punchier, neck
crak'n (we'll see what tuners do)
All in all, the N55 stock is a very satisfying, smooth and a powerful engine matching the previous one, IMHO.
I've had it less than 2 weeks, so i can yet go further in detail.
First impressions so far, have been excellent.
you'll definitely notice the single twin scroll turbo when driving
in the N55. it's distinctive yet subtle. As you're boosting u'll hear it.
The exhaust note, call me crazy, sounds different from the N54 one during
Wot. A bit more aggressive, stock.
And also, shift'n is so butter. The throws between gears are better
to me on the Msport N55 than the N54. The steering is a bit soft,
which surprised me a bit...Alot of body roll, kindy needs sway bars. I still need to break it in, so i can't comment too much.
I can't wait to get a tune in, I wanna see how far you can
push the N55 engine. I'm enjoy'n it stock and in no rush to do performance
mods. Hope this helps