How would i be able to tell the difference between say an hx35 and an hx40? going to look at an hx40 later today and would rather be safe than sorry

 

Well, hopefully it will have the tag still on it and it's still legible.

 

Measure the compressor wheel with some vernier calipers?

 

Check the data tag if one exists. It will show the type of turbo. If not, look at the general markings stamped in the turbine housing near the flange. An HX-35 will have a 12cm housing. An HX-40 will have a 16 or 18cm housing with a 4" outlet (IIRC) and a 6, 7 or 8-blade 60mm compressor wheel. If it's an HX-40 with a 7-blade compressor wheel, it's a hard to find Super 40.