By default, in Cheyenne, the header size limit for a post request is 102'400.
If you want to ajust this limit you can define the post-mem-limit parameter in the global context or in a specific webapp.
For example, to double the initial limit in the httpd.cfg, :
...
default [
root-dir %./www/
default [%index.html %index.rsp]
post-mem-limit 408'800
]
...