Here's something funny- the two intakes, K1 and K2, don't work the same with the same filter on them.
K2, the top one, was the one I was just testing the other day doing max up a steep hill. No evidence of air restriction whatsoever.
So this morning, before I head out for the dyno, I decided I'd put a foam filter on the K1 for the dyno run. Remembering how sensitive it was to the resistance of filter material when I was experimenting with it, I thought I'd reduce the resistance of the foam filter. The foam in the back of the filter is twice as thick as the sides. I flipped the filter inside out and trimmed some of the foam in the bottom/back of the filter to minimize resistance. Actually, I trimmed a little too much. The center, as you can see in the pic below, is so thin you can see the light through it. It's good enough though for a quick ride and a dyno run.
So, I put the K1 with foam filter on the bike. Head down the drive way- no problem. Turn on to the road- still going good. First long straight road I find I twist the throttle about 2/3rds. The rpms quickly climb then cough, sputter, cough. What the heck? Repeat and get the same result. The foam filter is way to restrictive for the K1. Yet it works great with K2.
Question: does the K2 move sufficient air but the K1 moves maximum air? My first thought was that there is a little less internal airspace in the foam filter on the K1. But if should move air better with the back thinned out.