I have the On3 headers and am about to install them. I bought the kit off a friend so no oil filter relocation or anything was included. I found out for myself today while wrenching I need either a relocation kit or he told me he ran a smaller filter. Was just wondering if anybody with the same headers have had luck with the smaller filter?? Engine is a stock block 308ci Ford. So FL1A is the filter I usually use. He claimed to use an AC Delco PF53. Thanks for anyone's input.

 

The Purolator L14670 is a couple inches shorter version of the fl1a, should be worth trying.

 

I don't have the on3 headers but ran into clearance issues too on my diy build. I ended up just getting the moroso or summit relocation kit, can't remember. Anyway it was like $40 bucks and let me move it. I did have to get a 90 deg fitting so I could direct one of the lines away from the header more than the kit allowed. I was actually surprised how much the relocation adapter still sticks out from the engine. With the supplied straight hose barb fittings it took up nearly as much room as the stock filter, hence the 90 I put on the one side. I was glad I put it in considering I ended wanting an oil cooler about 3 weeks later. Having the lines already there made that easy