The amount of restriction all depends on the turbo. The bigger the turbo, the less the restriction. It also has to do with the other characteristics of the turbo: ball bearing or not, a/r, trim, blah blah blah. You can turn some turbos with your breath, some you can barley turn with your finger. But none the less, the turbo does pose some exhaust restriction. It may be barley any at all, but it is there.