Head function - The plans of porting and flowing the head are for getting air flowing in to the engine although removing movement restrictions and turbulence. Some came with confined production head P8R which had 33mm intake valves (Ordinarily identified on VTEC B-sequence) vs 31mm intake (non VTEC B sequence), https://alexisbikln.blognody.com/28706496/a-simple-key-for-honda-b16b-unveiled