Read the commentary at the end.
Bottomline, unless you are running a monster drag motor, stock is better. ;)

http://home.usadatanet.net/~jbplock/ISO5011/SPICER.htm

P.S. A FIPK style may still give you a small power increase because it is feeding cooler air into the motor and not because it has superior flow. ;)

And I got this from a Titan board so I can't take credit for it. :D