Finally I managed to find the comparable foam filter material. It cost RM25 for 1" X 2' X 3'. So I cut out one piece and prototype installed it to the HKS cartridge. I have also snap some pictures comparing the OEM filter vs the DIY re-furbished filter. After installing it, I can feel Air pulling into the DIY CAI opening. Will drive the car tomorrow to feel if there is any difference. If this works then it would be very economical for me to DIY install the material to any filter cartridge (OEM needs to be cut and modify a bith to prevent the foam filter from being sucked into the intake. Currrent HKS have the green barrier designed to it.
Update 30 July 2009: I have tested the Filter, indeed the air pull is much greater but there is a trade off. Dust and small particle (especially water droplets) can sip pass thru it. So my conclusion is Sponge filter does have improved air flow but it can only trap bigger sand particles. Dust and water droplets may escape. My verdict is "Go back to OEM filter", it is cheap and effective to filter if couple with CAI. (CAI does direct more air but it also carry dust and water droplets).
