I don't think it would "kill" your engine, i think what he is referring to is that the 3.5" tubing of the intense FWI would be a little overkill for the amount of air the L27 is flowing. If i recall correctly you wouldn't get very smooth laminar flow through the tubing and it would actually hinder performance because your MAF wouldn't be able to get proper readings. I never really modded my L27 so i can't say from experience but i think others have recommended a 3" intake for the L27 over the 3.5" that is commonly used on the L67.
FWI - PEMs - DP - HF Cat - 3.4/3.5 MPS - 180* - PCM - 104'* - Shift Kit - UD WP - Solid Mount - DR'*
14.222 @ 95.27 - 2.112 60'