i was reading over the yotatech knowledge base thread about the ISR mod
and i am wondering why he used steel for the pipe, why not PCV or a 2.5 inch shop vacuum hose?

 

There are a number of folks that have gone with PVC from home improvement stores, some have even used flex tubing for household dryers. Using steel pipe, or really any exhaust pipe, simply makes the job look proper. Considering the price of the K&N FIPK kit, its a lot cheaper to do it yourself. Just remember to reattach your vacuum hoses after your all done.

 

This might give you some ideas...