and while were on the subject of velocity stacks....
this is a good idea for those of u thinking of changing to/upgrading your open pod filter... wat u can do is use ur normal 3" ram pipe...connect it to a
BPI Velocity Stack, then get an open pod with a 6" opening and connect that to it. this has been proven to give significant gains on the dyno...filters that has 6" openings include Blitz SUS, Blox, K&N etc etc.
The basic principle behind a velocity stack is to smooth out the air as it enters your intake. A normal air intake pulls air from all around the air inlet. Because air is a fluid, it will under all circumstances try and follow either a straight or smooth path. Given a straight, rigid entrance, the air entering from around the intake tip pushes inward upon the air entering through the center of the intake, following a fluid path as illustrated. This creates lots of turbulence and essentially lowers the inner diameter of your intake pipe at its entrance (Fig 1). A velocity stack, when added on to the entrance of an air duct, gives the incoming air a smooth path to follow into the pipe, allowing the use of the entire diameter of the intake, rather than just a fraction.
http://img30.imageshack.us/img30/8946/velocitystack.jpg
dyno chart sample from BPI website:
Its of a B18c1, first run is with a 3" AEM filter, second run with a BPi stack and K&N filter
http://www.bpinitiatives.com/images/test_03.jpg
http://www.8thcivic.com/forums/engine/223382-diy-bpi-velocity-stack-pic-heavy.html
ive seen dyno charts with even more gains than this... some up to 10-15 whp (mostly on VTECs)
this is also something im considering doing further down the road. getting the BPI (RM188) with a Blox filter (RM90) and later on moving to a Blitz SUS for easy maintenance.
my current HKS SPF already has its own velocity stack built into the unit itself... but bekside itchy mah lol
sample pix of how stack+filter looks like
http://img717.imageshack.us/img717/5500/0000bloxfilternvs.jpg
http://www.jonhsu.com/delsol/newam2.jpg