system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does a twin turbo engine actually work?

I understand how a turbocharger works, but when a car has two turbos, do they both work the synchronously, or does the second one kick in when more power is required? Are both of the turbos identical?
gpt
There are a few systems, but typically one is smaller and spools up faster, forcing the air into the second which is larger.

- The first turbocharger doesn't usually directly affect performance, instead it is used to increase the responsiveness of the second. This doesn't typically improve the final amount of boost much above that of a single larger turbo, but improves responsiveness. *End result: responsiveness, but not much extra power*

There are two other main approaches, though, where both do work together

1. Both are the same size, and are used synchronously or independently to either act as a single larger turbo, or to allow "staging" of the turbocharger power (ie half or full boost). This is slightly more responsive than one turbo, but not by much, but provides more boost than one turbo. *End result: lots more power, but not much more responsiveness*

2. One is larger and the other smaller, allowing the smaller to kick in earlier for responsiveness, while the larger gives a larger boost but with normal turbo responsiveness. *End result: More responsiveness and a moderate amount more power, although typically a more complex system*