No damage at all. I ran my gm 6.0 on 2 of the 6 quarts with a filter change and no prefill so more like 1.7 quarts accounting for the filter and lines last year and it never lost oil pressure when i was revving it near 3500 rpm and I even held it at that for a bit expecting the oil pressure gauge to stumble but it never did. Never made any lifter noise either. I let it idle back and watched it sit steady and quickly got down to hear the bottom end and heard nothing. Engines can run on a surprisingly little amount of oil.