This question is more suitable for SO than HN.
Given a four core CPU, if each request is lasting 30 seconds without I/O, then each request is going to use 1 core. On a 4-core CPU, you would only be able to serve 4 requests within a 30 second span. What is the request doing for 30 seconds? How much of it is actual CPU-bound work and what amount is I/O.