The difference between the FL1A and FL-1HP is the HP has a burst pressure of 400 psig where the 1a is 200 psig. Who cares, steel is cheaper than potatos, my
oil pump only goes to 70 psig when cold. The higher pressure rating is a ploy used by many filter manufactures to claim there product is better. The bypass is 9-11 psig on the 1A and 22 psig on the hp, once again who cares, my test show differential across filter is not even close to 11 psig. Filter media and surface area are the same on both.
All that being said the price difference is $11 so if you feel better skip a lunch and you paid for it, LOL. The problem with the HP is nobody stocks them, so you have to order and wait. Go to walmart and they will have about 15 1a's in stock.
I was impressed when I took the 1A apart, good bypass valve, I could not seperate the filter media at the seam, i think it was sewn and glued, metal caps, pliable anti drain back (not really applicable since my filter is mounted verticle).
Royal purple has answered my email, they have
synthetic media. The caveat will be when the bypass opends (9-11psigd) on the rp and if it is a clean bypass (yes). It retails for the same price as the fl-1hp or $15.00. Once again they waste weight with a heavy case. Edited, see post further down.