I'm not really a fan of airboxes, they always have side effects and although they can lower the inlet temp in a static situation (ie queuing for a start or on a rolling road, out on the go, they really don't make much difference. I say that with quite alot of testing experience to draw on! My engines rely heavily on inlet and exhaust pulse tuning to do what they do and the air box design can profoundly affect that. Although I've seen airboxes produce spiked figure improvements on occasion, I've never yet seen one improve the delivery overall and single entry ones, like plenums, don't ever sound anything like as nice as open induction. On forward facing engines I like to have a nice wide open airbox where practical, that doesn't impact the pulse tuning; example, here's our 205 hilllclimb car, which we did as much to split and manage the ingested air to the rad, as to the induction:
