When I wanted to rebuild my 1980 B21F engine I took it to a local machine shop who specializes in racing engines. I found I could not find oversize pistons so I bit the bullet and had forged pistons custom made. I noted they were noisy when I got back and installed the engine. The machinist told me that was characteristic of forged pistons. I accepted that. He also told me he fitted the pistons as tight as he felt comfortable with. Twice now, when driving at Interstate highway speeds (70 mph), most of the oil in the pan is pushed through the flame trap and into the filter box saturating the filter and winding up on the garage floor. When I keep the speed to 65 or under it doesn’t seem to develop this problem When I open the oil filler cap I can feel pressure. I am not sure what is normal so I don’t know if the pressure is excessive. I thought maybe the rings haven't seated but the odd thing is that it happens occasionally and not all the time. I drove all the way to Ohio from Virginia with no problem. Any suggestions on cause and what can be done to remedy this situation?