The original OEM turbos featured on the 2011-2014 Ford 6.7L Powerstrokes were a relatively new design idea for Ford, or should we say Garrett, the actual manufacturer of the turbo. This new design revolves around what Garrett calls SST, or Single Sequential Turbo, in which TWO compressor wheels are mounted onto a single shaft. This results in many of the benefits of twin turbos having great response off the bottom, coupled with a strong mid-range and top end. Unfortunately, though, this turbo design has also resulted in numerous failures, especially once modifications begin that enhance the boost levels the truck is seeing.
Because of the higher than normal failure rate, Garrett went back to the drawing board and released a revised version for the 2015-2016 model years. This version, called the AVNT3788, features a 61mm x 90.5mm compressor wheel featuring 11 blades and a 70.5mm x 62.5mm turbine wheel with 13 blades. The turbo itself is a double-sided compressor wheel stilll, deliving near two-stage engine boosting performance, all from a single turbo. For the 2011-2014 model year trucks, some will actually retrofit the 2015-2016 turbos on them, but it does require a complete installation kit when the current drop-in turbos as shown here for the 2011-2014 model years feature numerous upgrades that make the drop-in version favorable for many.
Finally for F-450 pickups, or all cab and chassis applications, Garrett has maintained the same turbo throughout all 2011-2016 model years. For those uncertain as to what a "cab and chassis" is, that would be a vehicle that came from the factory without a traditional pickup bed, also called a "narrow frame," as they are intended to be upfit with a flatbed, service body, etc.