I did the same thing a few weeks ago but i just started driving the stang this week and it made a big difference...I just have to figure out how to get the idle to stop hanging at like 1200 and just drop already.
I tried the mod and it created an ungodly howl at idle which rose in pitch as I accelerated. I'm going to try increasing the diameter of the hole a little and see if that makes a difference. It did drop the idle though.