I have run in to a a case where I lost all oil pressure suddenly on [forgive me ] a 355 chev. racing engine . during a qualifiying lap it dropped from 70 lbs to 0 . i came in and we checked it over .it would go up and down when reved to only about 10 lbs... turned out to be an imploaded oil filter . happened several times . I had to use an Oberg screen system and not over a 20-50 race oil to control it .