Over the years my fox has had the stock airbox with a K&N panel, a Denscharger CAI with a 9 K&N in the fender, and most recently an old school Moroso CAI elbow with the small 5 oval K&N clone Moroso supplies. I found punching numbers into an air filter sizing calculator ( https://streetandcircuit.biz/engine-...-filter-small/
) to be eye opening. Cliff Notes: The factory panel filter is correctly sized, the small 5 oval filters on every CAI out there are undersized, and you need a 9 long K&N conical to get the surface area needed for a NA 5.0 @ 6000 rpm.
I was looking for something different and ran into Corral user Thundetjet302s post about using a March Ram Air Kits airbox, enlarging the airbox opening to match the fender apron, and then not use the hose and scoop. You then have a 9 K&N with surface area close to the size of the factory panel filter, cold air from the fender apron, and an air box that is cleaner looking than the OEM unit. A little digging finds the March kit using a K&N 0810 filter (3.5 inlet ID, 9.0 long, 6.0 base, and 4 5/8 top) which I had in my spare parts cache from the Densecharger (AKA Home Depot CAI). You can still buy the whole March Ram Air package, but they will sell you all of the parts individually. This means you can source a brand new airbox ( https://marchperformance.com/accesso...r-ram-air.html
), pick up one off of eBay, or your buddy that got tired of cleaning leaves and road debris out of it years ago.
The March airbox inlet is an oval of about 5.0 x 2 1/8. I made a cardboard template of the factory apron opening and enlarged the March airbox to a 7 1/4 x 3 1/2 oval. This is very close to my apron opening which is now 8 x 3 1/2. I used a Dremel with a Rotozip but to cut through the 1/8 thick airbox and cleaned up the edges with a orbital sander using 80 grit sandpaper. The fender apron has seen a bit of Dremel cut-off wheel action and edge trim attached.
The 70mm Ford MAS mounts directly to the K&N and I needed a 3 x 4 hose to connect the MAS to my old school Tiny Avenger inlet elbow.
Thanks to Thunderjet302 for his posts about this mod. I hope the post helps somebody doing an old school NA EFI Windsor build.