I was just wondering how much boost you can run on stock internals for a 2000 civic si?

 

Depends what turbo. Your real question is "how much power can the B16A2 handle with stock internals?"

Then based on that information you figure out how much power you want to make. Then you compare turbos and how much PSI you need on each turbo to reach your power goal. Then based on that information along with what you can find for sale and how much you can spend, you figure out what turbo you are going to use.