they seem to be good on stock turbos with standard boost but try go over that and the dreaded creep sets in. im just in the process of modding my split dump and turning it into a bell mouth (a bit of choppy choppy), hopefully this works out and i can finally control my boost , if not i,ll be pulling of my exhaust housing from my turbo and opening up the waste gate hole a little and a bit of internal cleaning up to get more flow through there as well.