dj-lanevo3 : the compressor is the one that sucks air into for the engine
a bigger compressor fin , 16g , 20g ,46trim , 50trim are all diffrent size of compressor fin , the bigger the compressor and the better the compressor fin design is , the better flow of air it would make.
taking a small fin and stuffing it into a smaller compressor housing would reduce the efficiency of he turbo , so there are many compressor housing td05 , td06 , t04e , t04b , and such. compressor housing are measured in a/r for garrett and just plain names in mitsu's. if i take a 16g fin in a td06 housing let say and a td05 16g , it doesnt mean the td06 is gonna make a higher flow. in other way , if i take a 20g fin and put it into a td05 and a td06 , of cos the td06 will flow better cos its more efficient.
while the turbine side is for the exhaust. usually , the higher the capacity and higher range of rev u want, the bigger turbine housing u should get. in terms of a.r , usually 1.6-1.8 cars take 0.48-0.63 , 2.0-2.4cars take 0.63-0.84 or even bigger ones. getting a bigger turbine housing for a small cc car will promote lag , while a small turbing housing for a big cc car it will promote choke.