I installed JB4 several months ago. Some improvement, but not as much as I expected, so I went and dyno'd it. Did two runs of each Map 0 (stock), 1 and 2.
As I expected, not that much difference. When I sent the dyno and couple of data logs to Terry, he said my car was making an unusal amout of boost for stock. Not a bad thing I guess.
I just took my car in for oil change and coolant top up. Took me 30min to unistall. Going to drive it for a few more weeks before I put it back in. Had installed the cold air intake as well. Not going to reinstall it. A little too ricey sounding for me.
I Dinan'd my 08 335i and truth be told, it was faster than what I'm running now (N54 is king IMO). I'm debating going Dinan, but I don't think there'll be as much as an improvement because our cars already have the performance power package. I also don't care for throwing another 2k away when this lease is up.
2008 335i Dinan stg 2
2011 335xi se JB4 (current)