I have been told that with filter and pan a kevko can hold 6 quarts
Really though, what is "enough" is the question?
Enough is not dropping oil pressure through the lights or on decel and keeping the oil temp in a safe operating range for the oil you are using. I would prefer to have a little more sloshing around in there ( even if it cost me a little HP ) rather than run out at 7K cause I pumped the oil level below the pick up. You run out of pressure at 7K you WILL hurt the motor. Then the question becomes - how much you hurt it.
