Variable: special-display-frame-alist

Alist of parameters for special frames.
Special frames are used for buffers whose names are listed in
`special-display-buffer-names' and for buffers whose names match
one of the regular expressions in `special-display-regexps'.

This variable can be set in your init file, like this:

(setq special-display-frame-alist '((width . 80) (height . 20)))

These supersede the values given in `default-frame-alist'.