Hello Prateek

Anything more than 45% of total score is sufficient to get a good branch (maybe CSE) in an old IIT for an SC candidate.

I have seen SC people with AIR ~4000 getting CSE in IIT Bombay.

All the best :)

But, do not limit yourself to AIR 4000.

Unless you work hard enough to get AIR < 3000, you cannot guarantee that you will get AIR < 4000.