I bought a 1 series off a person that had this setup that was terrible that I reversed. I put a jb4 in at the end of fixing all the others aspects of car. The car now boosts whatever it wants really. Before the fixing it had a turbosmart electronic boost controller and held 20. I put jb4 with a mac solenoid and followed the guide for it. Top port of wastegate to port 2 of mac solenoid and the port 1 side of mac goes to bottom port of wastegate that is tee'd to the compressor housing connection. No matter what I do I get the same results. So I'm lost for words because on the tial chart the biggest spring rate is 21.75.