If you want the real deal then go here for the 90 degree elbow that is 2 1/2" on one end and 3" on the other. It is high temp rubber.
http://www.atpturbo.com/Merchant2/me...o de=SIL-90EL
It's on the bottom left of the page under 90 degree transition elbow. It's what I used for my turbo up pipe.