I have an extra set of the stock turbo's sitting around but the primary is bad. I haven't looked at them too much yet but from what I hear the impellers are different between the primary and secondary turbos. Are there any other differences? I ask because the turbos I have on right now are very high milage and if the current primary goes out, will I be able to put the old secondary in its place or rebuild the old primary with parts from the old secondary? Or will I have to shell out the money for a rebuild kit and any other parts I need?

 

There both Hitachi H12s, but they are different and I don't think that you could swap components between the primary and secondary.