i read performance GTi mag couple of weeks ago... (it wasnt mine though, my m8z!)....... and they did a test.
performance panel filter
induction kit cone type filter
stock filter with drilled stock air box
performance filter with drilled stock air box
and did power runs after each test, the drilled air box with stock fitler won!!! most bhp increase, also max power did this few years back and they found the stock air box with drilled holes to be better as well!!!
couple of years ago i drilled my XR2 air cyclinder, its made from metal and sits ontop of the carb. And the performance gains were better than when i had a cone type filter on there.
Im quite convinced the stock air box with 10mm holes tactically placed are better than induction kits etc. When the car manufactuer designs them they spend so much time and effort on most parts and what they have come up and designed obviously stands its ground, give it a little mod like some holes etc. and you laughin free bhp gains.
Obviously this isnt the case on all cars. Works well on cars i have had experience with from XR2, 8v Gti, 205 Gti, E30 Bm.
sorry to go on so much just a though lol!