Oil capacity for 5.7 L Chevy c20 van 1994?

With a STOCK oil pan, 5 quarts.

However... if anyone has replaced the oil pan or if the original owner requested a towing package from the dealer, it could be 6 or 7 quarts.

Change the oil and filter, add enough oil to bring the dipstick up to the full mark, then start the engine, (watch for oil leaks around the oil filter) and after a couple minutes, shut down the engine and check the oil level again. Bring it up to the full mark, and if you've been counting the cans of oil you should know EXACTLY how much your van holds.