Did some comparisons last time the car was on the dyno in october just to see how much restriction the stock airbox/filter was at “big” power. Here are the results. Seems ok to leave the airbox on at this point. The MAF likes the smoothing of the stock filter.
Nordic E85 tune, 3″ Nocat Downpipe, 2.5″ Catback, Huge intercooler, 630cc and 18t.
Pressure after the MAF in the inlet tube to compressor. Shown as Channel: Air1 P Unit: InH20. Boost Is Man P in PsiG. (23in/h20 is about .83psi)