you will get the same chatter as with not using a dump valve, the way to do it is let your foot off the throttle slowely then it will chatter without the dump valve, if you lift straight off the vacuum opens the d/valve allowing the air to escape meaning it wont reach the turbo to cause it to sltall/chatter. sounds really boy racer'y but you cant help but do it.lol escpecially when there is people aroung.

Oh the joys of owning a turbo (makes every 30yr old 17 again )