What oil do you use in your 1973 Pontiac 400 ci?

For a 1973 Pontiac 400 ci engine, it's recommended to use a high-quality motor oil with a viscosity of 10W-30 or 10W-40, especially if the engine is not heavily modified. If the engine has been rebuilt or is in good condition, consider using a synthetic blend or full synthetic oil for better protection and performance. Always check the owner's manual for specific recommendations and consider the local climate when selecting oil viscosity. Additionally, using an oil with higher zinc content can be beneficial for older engines to protect against wear.