a 18g is a mitsubishi turbo, you can find a compressor map online somewhere

but the term t3/t4 means like 5 billion different turbos/ wheel/ trim sizes.

You can have a t3 with a T04B with a 60 hifi compressor wheel
or you can have that ebay T3t4 which is a t04E with a 57 trim wheel
or this or that they keep going


what car is it going on and what goal power level, give details on both turbos and people will post up what to use