What is the Biggest Cam you can put into a Chevy 350?

That can't be answered without knowing what type of car it's going into. Is it a daily driver that needs to go through emissions tests? Is it a race car? Weight, axle gear ratio, transmission type and torque converter stall speed all matter a lot. But.............. to answer your question, you can put any size cam into a 350, because any cam made for a small block Chevy will fit. Drag race 350s can have cams with 260 or more degrees of duration (measured at .050" lift) and .700" or more cam lift. But that type of cam wouldn't run well at all below 3000 RPM.