I have a trim to fit prefilter on my Pop Charger. You can oil it if you wish, I just use it to help keep the bigger debris from getting lodged in the pleats of the filter. I don't recall the size or the part number but Summit Racing carries them.

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Jeb aka Ag Bullet
2001 Frontier S/C CC
www.nissanfrontier.net
My Ride
Most of the world's problems can be solved with blunt head traumas.