Came across this article wandering around the net and thought that it contained actual accurate results of the benefits of increasing the diameter of turbo exhaust systems to reduce back pressure closer to zero allowing the turbo to be more efficient.
http://www.superstreetonline.com/how-to/engine/modp-1102-exhaust-test-tech/
http://www.superstreetonline.com/how-to/engine/modp-1102-exhaust-test-tech/