[BiturboS4] Turbo change in pairs - can someone explain me why ?

[Steven Lin]

David  writes:

> Ok, I understand that if your car has 100 000 miles, and one turbo dies,
> chances are that the second one will follow in a short time. I understand
> that and old turbo will have maybe less efficiency than a new one, and
> mixing them would - maybe - corrupt the balance of the work of the 6
> cylinders. But if you have the one which fails fixed, and the other one
> carefully checked, by a specialized workshop, what's the problem ? That's
> what I'm planning to do, and it should be much cheaper than changing both of
> them.

The conjecture is that the second turbo was likely
shouldering the workload of both turbos when the first went out.  How
much are you willing to gamble on that second turbo?  It's the
opportunity cost of a second, future turbo replacement versus a second
turbo.

Besides, in one of their study guides, Audi recommends that turbos be
replaced in pairs.

Steven