if you figure out what turbo you have, you might just replace the turbine-housing (By changing the size of the Input vs Output on the turbine housing, aka A/R ratio).... thats alot cheaper than a whole turbo.
example: 1.25 A/R's on the turbine will give you alot of lag... and can ofte be replaced by 0.62 housing or similar, giving you a much quicker spoolup (by sacrificing some top-end power) .... if the turbine wheel itself is not "to big" though.
There is always a dog-tag of some sort on the Bearing/Core of the turbo....often with a serial-number, and a manufacturing number and so on... that's what you need to look for.
But if it says "TURBOCHARGER T3/T4" or some shit, it's guaranteed a poor Chinese copy.... and then you could just replace the whole turbo before it blows apart and damage your engine(as many of them do..)
