Pull the CD on N86851, it was approved with an ercoupe air filter. I would have thought that it would restrict breathing, but it seemed to run as good as any Franklin that I have heard . I have three different airfilters for Cruisairs, but none of them have ever been approved. One of them only filters carb heat air, another is a modified Cherokee 180 filter on a 165 Franklin, the other is a home made system that with a few refinements would be OK but who knows if anybody would ever approve it. If I ever get around to putting the 165 into my Cruisair, I will try to get the Cherokee one approved. I think it would be easier to get the feds to agree to a standard aviation filter with a few modifications, than a home made set up. I have been told that the Cherokees came with 2 different filters over the production run, and I dont know if this is an early set up or a late one. I got a new digital camera for Christmas so if I can figure it out, I will post some pictures._______Grant.