Originally Posted by Rescuer
i read it once before, but still learning so there is confusion factor.
read whole thread a 2nd time, am feeling more confident about it. will do this mod and drill the hole where it should go along that spine part.
i've also checked out your bullet TMIC mod which seems very very interesting.
It's good you took that the right way, more than one have ruined theirs by drilling in the wrong place, or by drilling too far into that "spine," as you call it. What is to be drilled through is an internal tube... and the hole is to be drilled carefully just far enough to enter the outside wall of that tube. That inner tube is an air channel between the bottom of the valve and the top of the diaphragm. After the plug is installed into the end at the bottom of the valve, the little hole that's drilled reopens that tube to atmospheric. The little felt piece over it lets it breathe but protects against entry of foreign matter.
And in response to the question earlier asked about why it wasn't done this way in the first place... It is, in a JDM model, but with a slightly softer spring. The ideal option for an STi is, arguably, the JDM part, if cost is no object. Personally, I think it becomes perfect after this mod.
Thanks for the comment about the BP Mod. You can find more info here