Holset HX52 help
 

Guy's I am trying to find somewhere to get advice on Holset turbos. Have I found the right spot?
I am looking at buying an HX52 unit with a 16cm turbine housing and 72mm wheel. However I will need like a 19-22cm external wastegate type housing or around there. What ever is common? I need to know if it will be easy to find an interchangeable housing or will I also need to get a different turbine wheel. Also are these larger housings easy enough to get hold of or not?
Alternatively is it possible to modify say a HX40 or HX50 housing to fit?

Thank you
Lee