Hey, Can anyone tell me what year sodium filled valves were introduced. I bought a blown 350 from a 1980 scottdale. The engine wasn't blown tho and it is now being rebuilt. When it came time for me to grinds valves and knurl the valve guides. the intake and exhaust are different diameters. I called the local automotive shop and they said thats because the exhaust wont wear as fast that way, and they are sodium filled. They didnt know what year this first came about, but they are pretty sure it was later than '80, si I know I dont have the origina engine from that truck. I am just curious, please tell me.