[harris_9]

I can't say whether it expands or not for sure. But in terms of air flowing through an aftermarket uicp vs stock; I'm pretty sure there is a portion of the stock uicp that is reduced in diameter. Whereas the metal aftermarket uicp's are the same size the entire way through.. The section where it reduces down has to slow air flow to a certain extent anway.

 

[harris_9]

The aftermarket pipes reduce in size too, due to the fact that the small side has to be the same size as the turbo outlet.

Yes I remember that. But I think there's another place mid-way through the pipe that reduces again if I recall correctly.