Porting and Clipping

"Porting" is a term for using a grinder to remove material and smooth the passages in the turbo. It improves air/exhaust flow at all rpm ranges.

"Clipping" is a process where material is removed from the exhaust turbine. This reduces the fin area exposed to the exhaust flow, so turbo lag will increase slightly. But at high rpms, a full turbine wheel will actually choke off exhaust flow, so clipping can dramatically improve high-rpm horsepower.