is that a 4% increase in airflow or a 4% drop in air intake temperatures? the charge air is heated up when compressed by the turbo and then passed through two intercoolers so in my humble opinion i can't see why having cold air go through only to be then heated up then cooled down again is so important. does the MAF measure just airflow or the temperature of the incoming air?
Airflow.
The effectiveness of the mod'd airbox can be see by logging MAF readings of g/s of air coming in.
Mine increased a huge deal with a mod'd airbox, whilst only marginally with a BMC.
It really does work, eveyone that has done and logged the results has amazing results.