The exhaust manifold is the first collector system for the overall exhaust system, and is also the hottest part of the system when the engine has run for a while. They may combine all at once (at a single point) or gradually collect in sets, depending on the design and room available.
High Performance Headers
Headers are a popular upgrade option due to being relatively easy to install them (the engine don't have to be taken apart) and the low cost-per-horsepower gains.
Pictured at the left are parts to a header set for V6 in a front wheel drive drivetrain layout. Because the engine is positioned sideways, one exhaust manifold is at the front and the other is in the back, so the two headers are shaped quite differently. Also in this design, the collectors gather the sets of three, then combine the pair.