[VIDEO=youtube;azPKIjxmmdU]https://www.youtube.com/watch?v=azPKIjxmmdU[/VIDEO]
So... think this video applies to Turbo cars? What are the implications with introducing a turbo into the exhaust stream?
It comes down to flow and velocity vs pressure. Low pressure or in terms of piping can cause low velocity. Think blowing through a large straw vs small. Your main objective is flow and if your exhaust has enough velocity this isn't an issue but if it doesn't then you loose power. Before and after the Turbo are two different things and before the Turbo is more important in terms of velocity. The proportions have to be correct or you will loose power or response. It is not as easy as bigger is better.
This is kind of complex and I don't have a PHD in thermodynamics but there really isn't a simple answer as to what gains are had by modified exhaust. N/A is also very different for a Turbo. You can get by with certain things on a Turbo you couldn't on an N/A engine. I'm sure scrounging the internet will verify this with dyno charts and when bolting on parts with a Turbo vehicle you can usually see gains everywhere. On an N/A engine it is give and take usually with a trade for TQ over HP. Goes back to flow,velocity, and pressure except on an N/A engine you are using atmospheric pressure and thus why you see a trade off.
Basically to me that video showed the headers are more then enough to support the flow of that engine. They are also very simple in design, start adding crazy bends and loops and the results may be different with collapsing tubes and disturbing flow. There is a point of diminished performance it just wasn't met.