OE: The OE part has a 50mm (1.94 inches) butterfly.
The open end toward the turbo is slightly larger at 2.10",
but this isn't important.
Aftermarket: The stock TB is much larger than the turbo outlet,
it is also the one that the EEC is calibrated for. Changing to
a larger bore will cause lean WOT and will not increase max power.
Modifications: Probably none is required; however blending
the surfaces never hurts. Putting a full radius on the leading
edge of the butterfly and a knife edge on the trailing edge may
help. Grinding the screw head lower and reducing the throttle
shaft thickness also may help. When grinding on the butterfly,
DO NOT grind the edge itself otherwise when it is closed it will
allow too much air for idle.
