Only one manufacturer claims that there are 3 actual stages with a stock turbo and it's pure bullshit.... You can have an upgraded intercooler ("Stage 2"), hybrid turbo (real "Stage 3") or big turbo ("Stage 4")... As far as the original question, yes, actually for Cobb's "Stage 3", they do say you're supposed to have a high flow or catless DP but all you really need is at least the intercooler.