If you drag race and stuff, yes it will help as it will relieve compressor surge. No you won't hear it between shifts in an auto because the throttle plate has to close before the blowoffs will open. If you have a friend with a 5spd turbo car with a blowoff, ask him/her to floor it and let off a couple of times. You'll see that every time the throttle is letoff, the blowoff goes off.
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