I couldn't find a lot of info on this when I was looking, so this post is for posterity. This particular application is a 1991 4.9L. I think this is a good reason to stick with Motorcraft:



The PCV valve on the left is Motorcraft EV111; in this application for a F150 RWD under 8,500 GVW. The supposed Fram equivalent FV243 is right beside it, the second from the left. Third from the left FV209 is for over 8500 GVW. on the right is FV246, the Fram equivalent to Motorcraft EV118 (for F150 4x4).

Although I cannot measure spring rate, the FV209 has the weakest.

On the three Fram valves, all three plungers are the same. They all have the letter "F" stamped on the bottom. As far as I can tell the only difference is the spring weight/rate.

The plungers between the EV111 and EV118 are stamped differently. The EV111 plunger is stamped "L" but the EV118 is in my truck now and I can't remember what letter was stamped on it, I just remember it being different. I would assume that since the plungers are stamped differently that there is a dimensional difference of some sort.

The inlet holes (bottom pieces in the picture) on the three Fram valves measure .322" and the Motorcraft measures .328". The Fram plungers measure .287" on the large diameter, and .198" on the small. The Motorcraft plunger measures .297" and .168", respectively. In the upper half of the valve body (the top pieces in the picture) the hole that receives the plunger measures .308" on the Fram valves and .310" on the Motorcraft.

Hope this information is useful for those of you searching.