all of the parts that wear out or become worn are replaced when you hiflow a turbocharger
- bearings
- wheels (exhaust and compressor)
the exhaust snout is bored out and a larger compressor wheel is fitted (new also).
so it can flow more exhaust gas and drive a bigger wheel. a new larger compressor is fitted.
which in turns drives more air into the engine (hence power increases).
finally its all balanced out to make it prefect at 100,000+ rpm.
the only parts that are retained are the housings, and main core.
this is because there is no need to replace or change them and it only adds more cost, plus it wouldnt mate up to the std items if the housings, flange etc changed.
so a highflow of a turbo does two things
- service of the turbo
- increase power
if you organise a std service/recondition of the turbo they may just replace the bearing pack (commonly known as a CHRA) and balance it again
i am insure if they would replace the exhaust and compressor wheels at a 100,000 km service for example