The standard Corvair oil filter as a special mount where a bolt goes into the end to hold it in place instead of threading it over the nipple that leads to the engine as in most cars.
This arrangement limits the availability of filters, The only real Corvair filter I have seen is the one that came on my engine (first picture).
Clark’s and many other Corvair parts suppliers and stores sell filters made for the Corvair. These first two pictures are just a couple of examples. I have not seen or tested either of them.
Since I did not want to depend on my suitcase and trips to the US for filters, I bought an adapter sold by the Corvair parts vendors. This adapter allows the use of a number of different generic filters. This adapter has a 3/4-16 thread.
Since the Corvair has its own relief valve in the block, rated at a 10 psi pressure differential, it is not necessary to have one in the filter, but in case that valve clogs or does not open, it is not a bad idea to have one in the filter as long as it does not open before the standard one.
Since I wanted the highest quality filter available, I limited my selection to those made be Donaldson. I set out to determine the best possible filter that would fit the adapter, so I measured the minimum and maximum diameters for the gasket seating surface. Looking through the Donaldson catalog, this reduced my 3/4” selection from 40 possible to 28 possible.
The next step was the diameter. Any filter over 3.25” diameter would make it hard to change the fan belt, so that narrowed my selection to 7 possible filters, eliminating the synthetic P16071 that I was considering.
So then I looked at the length. Since I am using this in a vertical position (there are 90 degree adapters also) any filter longer than 4.25” would not have room to screw on, so that reduced my selection to 4 possible filters.
I have selected the P502016. Here you can see two pictures of one used for 5000 miles of taxi service in a Toyota and another in its original wrapping and box. Here is how it looks installed in my Corvair.
For those with the horizontal adapter, the P554770 is an extremely efficient filter and would be my first choice.