Several issues…
A turbo will spin over 100,000rpm. In some cases over 150,000rpm. Poor balancing or tolerances of parts will result in cartridge failures
Then there is heat. Poor quality metal/material that is used in a lot of copy turbos, is just that – poor quality. Put 600 degrees through the exhaust housing, this heat is obviously transferred to the turbo core/bearings, which overtime fatigue can set in.
And then there are the wheels… They are using ‘70s & ‘80s wheels from the T04… Garrett GT wheels for example have undergone significant redevelopment since their earlier versions so offer better flow and spool for a given target, all of which improves performance.
Then move onto the seals and surfaces not being perfect. Another failure point over time.
The main issue with a lot of the China turbos is the consistency. 10 turbos might be fine, 2 maybe not so.
If you happen to purchase one of the 2/10 that fails after 1,000kms, even 5,000kms – You’ve gotta pull the setup apart, buy another turbo. So you are already behind as it’s now cost you double (new turbo), and it’s also cost you time to replace it all.
The poor man pays twice – Seeing it more and more these days here on SAU unfortunately.
All well and good for a new product to come along and it be tested by a few people… Unless you can afford to do this however, spend the money on known products first.