The subaru community has believed (myself included) for a long time that the stock turbo on the WRX was a TD04L-13G. This was based on statements made by well respected members of the community back in early 2002 when the car first came out.
The DSM community has been refering to it as a 13T for quite some time now, and since I just recently pulled my stock turbo off, I just pulled the compressor cover and measured the compressor.
According to compressor dimensions published on :
The compressor impeller measures out as a 13T, not as a 13G.
My compressor measures 2.205 inches at the max diameter across the impellers, (exducer dia) compared to the expected 2.203 inch max dia on a 13T impeller.
The minimum dia across the impellers (inducer diameter) measures 1.599 inches compared to the expected 1.597 inches for a 13T impeller.
This shows a consistant bias of +.002 on the measurements ( using a very old vernier caliper that has not been calibrated in 25 years.
It looks to me like we need to begin the long process of changing the urban legend that this is a 13G impeller because mine at least certainly measures out as a 13T.
I suspect the basis of this is it is nearly impossible to find a compressor map for the 13T, and folks used the nearest thing they could find, and it took on a life of its own.