Originally Posted by 6spd

I saw a third party chart years ago comparing the flow rate and filtration of of a handful of different air filters (for an S2000) and the results were pretty much as follows: Stock filtered best but flowed worst; K&N filtered second best only to stock, but flowed very well; HKS flowed slightly better, but filtered very poorly; Apexi flowed poorly and filtered poorly; and the other 2 were honda specific companies. I wish I still had the chart because I wanted the HKS filters back in the day but strayed away after reading the results. Whether these findings hold up on the Z, IDK. Hope this helps!

Also, the difference between the filters will not be tangible because changing only the filters makes such a slight difference overall. Better safe than sorry IMHO.