I did a variation on the mod. I cut off the FRONT portion of the bolt between the screw threads and filed down the portion outside of the screw threads to almost nothing. That way, the screw threads are still there. (The mod as posted calls for the REAR portion of the bolt to be cut off, which is much easier to do.) Now, the incoming air can glide up the center of the butterfly plate without the bolt disrupting the air. ( If I had a threader and the right size screws, I would cut off the whole front portion and thread the rear portion and screw in the new screws in from the front instead of from the rear.)
The result? Amazingly, the lull before the midrange pull seems to go away earlier. (PLACEBO??? -my disclaimer) But, it doesn't turn it into a SR20det. But, hey, it's a free mod, so anything noticeable is good! Also, the SOUND changed considerably. (I have CAI) The whooshing sound at WOT was diminished 75%, and the tone is much more refined and very much less raspy. (I think the bolt semicircle profile over the butterfly plate causes a whole lot of turbulence, thus causing the whooshing sound.) It is so much less raspy that it seems to sound quieter and deeper.