I've been reading on the Singapore Copen Club regarding drilling holes in the back face of the air box to increase air flow. (you might need to be a registered member to see it). http://www.phpbber.com/phpbb/viewtopic.php?t=2364&mforum=copensg I've also seen this product on yahoo auctions. Which seems to confirm that holes in the back face give a benefit. Be it increased performance or induction/BOV noise. http://page19.auctions.yahoo.co.jp/jp/auction/x176828634#enlargeimg Has anyone tried this? Does it make any difference?