When you use 4" is acts like a charge pipe.

Also there is NO ISSUE with oiled filters, none, nada, zip, zilch. The only time there is ever a problem is when people clean them and reoil them and put too much oil on themselves. That is not the fault of the filter. I have been running oiled filters for 13+ years and have never had a MAF problem. I know many, many people who run oiled filters and not one of them has had any issues either.