What is a Twin cam?

A twin cam is an engine that has two cam shafts (which open and close the valves). The most common reasons for two camshafts are: If a V-shaped engine design uses one cam shaft for each side of the V - obviously, if a V engine has overhead cams, you would need a cam at the top of each side of the V. Also, a straight in-line engine with two intake valves and two exhaust valves per cylinder might use twin camshafts.

Actually, I V-6 or V-8 engine with one camshaft on each head in a overhead cam configuration is still considered a single overhead cam. The only time an engine is classified as a twin cam or double overhead cam is when there are two camshafts on each cylinder head. A double overhead cam V-6 engine would have a total of four camshafts. Two for each head.