I have the TurboXS BOV and I didn't put any washers in. I experimented with 2 washers and ended up with a check engine light. P0172...Right Bank Rich. I think low rpm driveablility suffers a great deal with the washers. If I didn't step on the throttle enough before I let off, the turbo would back-spin. This is very bad for the turbo. I would recommend no washers until you are running enough boost that the BOV might leak and you NEED more washers to stiffen the spring.