i have never done it ( not yet). this guy is a reputable member of clubWRX who moved on to other cars. i prefer to keep his name quiet so he doesnt get any flames. he told me he used 2 washers on his BOV spring. he also told me that most people use 3-4 but 2 worked fine for him. a guy at a local performance shop does the same thing but uses 10? LOL! he says it works great for him so whatever works on his race car (its a track car only).