Originally Posted by bram

anti surge inlet has absolutely nothing to do with letting air into the turbo. Its all about letting air out of the turbo during surge conditions. Ie when the turbo is spinning fast, but the engine air demand is low. (like when youve just boosted hard, then you close the throttle) if you look at a compressor map, the left most edge is the area of compressor surge. Having anti surge holes/ports extends that a bit by allowing some of the compressed air to bypass the engine back into the turbo inlet. So your turbo can be spinning fast, but not supplying as much volume of air if needed, without the turbo surging (stalling).