It’s a bit of a bummer that the pan is installed already. Otherwise I’d say, before installation, figure out how low the crank is or windage tray is in relation to the pan rail and then transfer that into the depth of the pan to mark. Then fill the pan a quart at a time with water, no sense using oil at this point, to find where 4,5,6 quarts are in the pan.
From here you can figure out the new parking on the stick or where the oil sits with *** amount of quarts sits on the stick. If 5 quarts is s on the low mark, I’d call it good to go since it’s a quart more than stock and it sits lower than a quart down vs a stock oil pan with an additional quart inside.
Do you happen to run an external filter and/or cooler?
