How to change kernel i/o buffer size

I am running some experiments with I/O intensive applications and am trying to understand the effects of varying the kernel i/o buffer size, different elevator algorithms, and so on.

How can I know the current size of the i/o buffer in the kernel? Does the kernel use more than one buffer as need arises? How can I change the size of this buffer? Is there a config file somewhere that stores this info?

(To be clear, I am not talking about processor or disk caches, I am talking about the buffer used by the kernel internally that buffers reads/writes before flushing them out to disk from time to time).

Thanks in advance.