What are double over head cams?

Question

what are double over head cams?

Answer 1

A cam in an engine is used to open and close the valves.  There is one cam per valve.  Usually, they are below the cylinder heads and open the valves via rods.  On an overhead cam, the cams are up above cylinder heads, they do not use rods and are turned by chains.  A double overhead cam (or DOHC) has one cam assembly per bank of cylinders, i.e. on a V8, one on each side of the 4 cylinder bank on each side of the V.  DOHC improves engine performance.