Strange user name...Facts Only wrote:If you are referring to 2114 and F1 teams then they don't choose the exhaust diameter.
The engine suppliers design and make the pre-turbo exhaust. As for the the tail pipe there is a maximum diameter and a very narrow box that the exit can be placed in, the diameters are to the maximum value and the length is set simply by how long it needs to be to go between the turbine exit and the tailpipe position box. There will be some parameters such as bend radii set by the engines suppliers that will be given to the teams to make their tailpipes.
This is not really factual. The teams can design their own turbo headers, it depends on what they agree with the engine manufacturer. All the Renault teams had their own unique turbo header design. On the other side of the coin, Mercedes and Ferrari that did not allow their customers to use a turbo header of their own design for a number of reasons. Maybe in 2015 we might see that restriction removed?