Thanks for posting that. Did your car have a Check engine light on when it went in for service?
Two things I noticed after running the part numbers through realoem to see what they actually replaced on your car....
The crank case breather valve should not have any impact on power output from my understanding of what it does. Here's a pic of the part...
Essentially all they did was replace two intake to turbo gaskets shown here
(item 9).
http://realoem.com/bmw/showparts.do?...13&fg=20&hl=13
Simple part that is easily replaceable/checked but I find it strange that it could leak there. That area does not see Boosted air at all. That is pure vacuum where the engine is sucking in air from the intake filters. Plus the only way I could see that having an impact on output is if it is letting in "un-metered" air into the system causing the ECU to freak out. Plausible I guess but worth another 40whp/wtq? I am going to check my car tomorrow and tighten the clamps there just for good measure.
Also these gaskets are not unique to the N63TU from what I could tell so if this is a problem area for tuned cars I would expect to see the same issue pop up for pre lci 550's as well.
I plan to go back to get another run at the dyno now that I'm back on my summer wheels/tires plus new 3" exhaust. Too bad it will never be apples to apples comparison since I am the only RWD tuned 550 on that dyno and I'm not sure if there are any calibration variances on the dyno settings between RWD and AWD
Alan