I have a bunch of holset hx40's I'm trying to sell but how do i figure out the exhaust and compressor housing size, they aren't marked like my borg warner stuff. i just see a bunch of numbers

 

I know the turbine has the cm2 cast inside them usually.

 

inside the exhaust turbine or where exactly? I'm very un familiar with holists and don't want to give out wrong info so the more detail the better

 

Yea, inside the turbine just above the inlet. If theyre dirty or rusty u mite need to wire wheel it to see them. Commonly on an hx40 if its a T3 divided footprint it will be an 18cm2. Of its a T4 style divided footprint they came in 17cm, 19cm, 21cm, and 23cm... maybe even 25cm.
There is a conversion chart from cm2 to a/r over @ dsmtuners.com but idk how accurate it is. As for the compressor a/r I dont even know if holset gives those measurements. Holset covets their specs and compressor maps like theyre an international secret lol.
Running those casting numbers never turned up anything for me with my holsets. Btw, if they ate genuine holset hx40s, you can get an easy $200/ea if you find the rite buyer. Amazing turbos for a healthy v6 or great twins for a decent v8. Lots of dsm and honda guys use them also