The argument is that the Porsche filter is finer so stops all the little particles and it doesn't matter if the box holding the filter has holes in or not - it is the filter doing the work not the box. The K&N filter is slightly coarser so lets particles through. As far as I am aware, though, this has not been proved. The question is, though, do you want to risk it for a slight improvement in induction noise?
You pay your money and take your choice....
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