are headers and exhaust manifold the same thing?
They have the same basic function of collecting the exhaust gasses out of the exhaust ports of the block and funneling them down towards the cat/muffler etc. The main differences is that an exhaust manifold is usually a big rough cast piece of metal with exhaust passages cast into it, whereas headers are usually painstakingly welded together from sections of pipe. Headers area often designed in such a way as to have similar lengths of piping for each cylinder or specially tuned lengths to take advantage of pressure wave tuning and tend to look like a nest of snakes rather than a big solid cast manifold. The pressure wave tuning and flow benefits of headers are beneficial to high performance applications where cost is less of an issue.