Originally Posted by Spooler

The AR is talking about the exhaust housing to intake housing size. T-2, T-3,T-4. T-6 are the housing sizes. That is the frame size of the turbo. Garret GT2860 is using a frame size of T-2. Garrett GT3076 is using a T-3 frame size. The frame size dictates how large the housing is itself. The larger the frame size, the larger the housing. You can run a larger housing with a tighter AR and get more power. That's the simple version.