Just installed a homebrew FIPK type air intake, a K&N Drop-in Filter into the OEM box, added a 4" deckplate (hole w/ cover) to the bottom side of the airbox, and cleaned the MAF and Throttle Body.

HOLY CRAP!

I just unleashed some ponies and some much wanted GROWL!

Of course I can't quantify how much, but I can say that it's very noticible. I'll post up some pics tomorrow, but it's basically the stock airbox w/ a re-sealable hole in the front which feeds to the throttle body via a custom intake tube.

The tube is a 3" rubber coupling, a 10" piece of 304L SS Sanitary Process Tubing, and a 3" 90* Rubber Elbow.

Total cost:

Filter - $54
Rubber Coupling - $8
Rubber Elbow - $9
10" piece of 304L Tubing - Freebie from the scrap pile @ work.

Idle sound is pretty much unchanged w/ the hood shut. Get on the throttle a little (1800-2000 RPM) and you can just start to hear it. Open it up and it's a NICE deep V8 sound with a MUCH improved throttle response. While I'm taking pics tomorrow, I'll get a vid clip at WOT as well.