Don't want to ask a stupid question but- Why the difference in capacities for the 389 and the 400 and up? As I understand the Poncho block it's the same pan, what am I missing thinking about that would jstify the added quart?
yes they use the same pans but the 400,428 and 455's have better oiling systems and thus can handle the added capacity. You can open up the oil galleys and ports in the rotating assembly and lifter galleys to handle more pressure and capacity.
60Buickrod if your brother has any kind of oil pressure and is running a Pontiac he will eventually blow out the rear seal as it is a rope seal and will only stand so much pressure before it starts leaking constantly. The only way I would go more than six quarts is with a remote filter setup and oil cooler then would have to give alot of thought. Like I said I normally run 5-6 in my 400 but normally 5 with a Melling pump, stock pan and full length windage tray. If your brother has ever been in the engine and didn't put the bottom section of the dipstick tube back in through the windage tray then that could be one reason why it doesn't read right. Another could be it has the long top tube for an A/C equipped car and the short non A/C dipstick. The only other way to increase oil capacity on a Pontiac is to change to an aftermarket pan. Then you would need to run 7-8 quarts of oil.