CT12 (1G) Compressor Wheel:
Click here for pic
CT12A (1J) Compressor Wheel:
Side by Side:
http://www.toymods.org.au/1G_vs_1JZ/images/1J & 1G Compressor Wheels.jpg
here are the sizes:
1G turbine inlet = 25mm
1J turbine inlet = 30mm
1G turbine exhaust outlet = 42mm
1J turbine exhaust outlet = 44mm
1G compressor inlet = 31mm
1J compressor inlet = 38mm
1G compressor outlet (to intake manifold) = 29mm
1J compressor outlet (to intake manifold) = 29mm
Click here for pic
CT12A (1J) Compressor Wheel:

Side by Side:
http://www.toymods.org.au/1G_vs_1JZ/images/1J & 1G Compressor Wheels.jpg

here are the sizes:
1G turbine inlet = 25mm
1J turbine inlet = 30mm
1G turbine exhaust outlet = 42mm
1J turbine exhaust outlet = 44mm
1G compressor inlet = 31mm
1J compressor inlet = 38mm
1G compressor outlet (to intake manifold) = 29mm
1J compressor outlet (to intake manifold) = 29mm