Originally Posted by 318 NewBoy
Manifold is where the fresh air will be directed into the engine. Header is where the exhaust gas will be directed out of the engine.
The words manifold and header both mean pretty much the same thing: multiple ducting pipes condensing down to one or one pipe splitting into several. I've heard people calling an intake manifold an intake header and an exhaust header an exhaust manifold. It's just which side of the engine that makes the difference.
There apparently is a small difference between a manifold an a header, at least on the exhaust side. I'm not exaclty sure but a factory car usually comes with an exhaust manifold and if you go aftermarket you can get headers. Semantics aside they are esentially the same.