[Domonicdave]

If I understand correctly, they changed the 550i motor to a N63tu for cars build 8/13+. I'm looking at all these 2013 on line, and many of them don't specify the hp. Is there something that distinguishes the N63tu motor from the N63 (exterior style or designation in the VIN)?

[BimmerV8]

the N63TU engine for the F10/11 was launched in July 2013, thus along with the release of the LCI (Life Cycle Impulse = facelift model). the output is 330KW (Kilowatt) or 449 hp (continental Europe)/ 440 hp (US); torque 650 Nm (480 lb·ft) The modifications compared to the N63 are material.

[Pimpsy]

The switched over at the very end of July. My 2013 was built on July 27 and I think was possibly the very last n63 built, or very close to it.
You can run the VIN and it will tell you which engine is installed if you aren't certain.

[mness]

The n63tu (445hp) started with the 2014 model year F10. If you're looking at 2013 model year F10's, they're the n63 (400hp).

[550Reasons]

I believe some late late model 2013s have it ? not 100% sure
but I know for a fact any 2014s have it, plus they also got a facelift, so Id got with a 2014.