[40cpe]

I put a gauge of both sides of my 95% filter and it read 10# lower on the out put side. It takes ~ 10# to open the bypass. The Wix filter shows a flow rate of 7-9 gpm, I don't know what the output of a flathead oil pump is. There is no difference in a modern engine, I think they all bypass some. No proof, just an opinion.