So I know this has been discussed and I'm still getting acclimated to my 07 335i with JB4 map 5 and DCI for now. Anyway, I've done some searches and it seemed like a lot of people were having a hard time shifting into second at or above 6k RPM. I tried to do some more research to see if anyone had found a solution before I posted this so please forgive me if I'm repeating anyone else. This is from my own personal experience, which I don't have a ton. I'm Still learning. I noticed before I installed the JB4 I wasn't having this issue or none that I noticed until I got the extra power from the JB4.
With the the DSC on (mode the vehicle starts in) or DTC on (push button briefly) the car would shift fine at or above 6k RPM. With DSC completely off (pushing button for about 4 seconds) the car would not let me shift into second. I was clueless at first until I knew it couldn't be a synchro bc I'm not even getting a grinding noise and bc with the DSC and DTC on it would shift fine at those RPM's. So I toyed around with the DSC completely off. I noticed if you have your RPM's bouncing up and down the rev limiter the transmission or computer locks you out from shifting into 2nd, I'm assuming this is to protect the transmission from absorbing too much shock, but under a more controlled or consistent RPM it will let you throw it right into 2nd without much force. I did a few dig runs to test this out and it worked fine. The first few runs I went all out and just dropped the clutch and let my RPM's bounce around until it wasn't bouncing off the rev limiter and I had no problem shifting. The other runs I toyed around with feathering the clutch, which would be the more proper way to do this to control the RPM's better. Both of the techniques I used seemed to work fine for me. It seems to lock you out from 2nd if you have excessive wheel spin, which is why it would make sense with DSC and DTC on, it works fine shifting into 2nd bc the wheel spin is more controlled. I know with DTC it still allows most wheels spin, but it's still more controlled. So essentially I guess I'm letting the engine and transmission catch up to each other. Maybe there is a proper name for this?
Anyway, I thought I'd throw that out there and maybe it will help someone. I'm no expert with terms and don't claim for anything I said to be completely accurate. I just wanted to speak from my own experience. If you have your own technique share it please. If you have done this and it solved your issue let us know. It definitely solved mine!
Thanks for reading!