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.
Setup:
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)
Runs 6,5 Airbox Open No filter Just the maf. But using stock airbox lid so there is no MAF scaling influencing things.
Runs 1-4 Stock Airbox and filter