Gravity casting using sand molds were, like you said, just how you did it until that time. Dad had an early 90's Saturn SL, and it's engine used the lost-foam c

Gravity casting using sand molds were, like you said, just how you did it until that time. Dad had an early 90's Saturn SL, and it's engine used the lost-foam casting process. You could see the surface texture in the metal from where the polystyrene had expanded when it was made. Sand molds weren't able to show a feature that fine. https://en.wikipedia.org/wiki/Saturn_I4_engine https://en.wikipedia.org/wiki/Saturn_I4_engine https://en.wikipedia.org/wiki/Lost-foam_casting https://en.wikipedia.org/wiki/Lost-foam_casting