I was having some surging issues and decided to replace my MAP sensor (got one very cheap). After replacing it, I saw something I didn't expect... better boost. I'm hitting the wastegate on my HX-40 now very quickly and at a lower setting on my PowerMax. I haven't played with it much yet but it's definitely more boost and faster response. As far as the surging, it's still too early to tell if this took care of that issue. Just thought I'd pass it along...