Flighter
fordsy
Here's the advice from my engine builder who put my pinto bottom end together which i'll be taking over pretty much anyone else out there.
"oil needs to be a mineral based 20W/50, 25W/50 or 25W/60 NO synthetic can be used."
Did he explain why?
He did at the time but I can't remember precisely why so I won't guess. I've had the head and bottom end done by two people with good experience with pintos in both race and road and both suggested the same oil type (mineral) and weight (as listed above). That's good enough for me.