The turbo outlet is 2.5", but the airbox outlet is 3". You can use a 3" pipe and at the turbo you can use an elbow that's 3" on one end and 2.5" on the other end. This place and others sell them.
http://www.stealthwork.com/reinforce...bow-p-307.html
Here's a pic of an uppercharge pipe that a guy named Adam makes. It will give you an idea of what it looks like.
http://www.prototypepower.com/go.htm