Gary
I replaced all my intake ducting with components from intakehoses.com. on a ISX 525 Cummins in our 07 Executive, AFTER the 5 year warranty.
I did a lot of research and talked to a lot of knowledgeable people on the subject. That ducting causes air friction due to its construction and bends in it as used in our coaches. Class 8 trucks do not use it. They ALL use rubber fittings and/or aluminum tubing, which i purchased from intakehoses.com. That is what i converted to, and i will tell you the difference in performance was great. At that same time, i replaced my muffler with a straight thru resonator from dynaflexproducts.com. They are the largest MFG. of Class 8 truck exhaust components in the U S A. I also replaced the OEM Air Cleaner with one from AFE, Advanced Flow Engineering out of Ca. The A C is not on their web site . You have to call them. Overall performance was great and fuel economy went up 1 MPG "cruising". Bottom line; More CFM of air to engine, and NO back pressure in the Exhaust. And NO negative effect on Turbo. I did all of the above in 7-2011. The photo is of the Aladdin screen during one phase of traveling we did.
I cruise at 60-62 MPH, 1350 RPM.
Paul A