My brother with a crx, b16a turbo gained 65 more hp without air filter.
My bother in law picked up something like 60 plus hp with filters installed on a 383 tt, no intercooler, meth injection. The car is a donor.
Only assumption, with steve the air flow was less turbulent with filter,and my brother the filter acted as a restriction, or caused tubulence. Both were KN filters, not the same model.
I'am not an expert just adding information I've run into.