To prevent vim from auto-wrapping at column 80, try:

:set tw=0
:set textwidth=0

or

:set wrapmargin=0

'textwidth' 'tw'        number  (default 0)
                        local to buffer
                        {not in Vi}
        Maximum width of text that is being inserted.  A longer line will be
        broken after white space to get this width.  A zero value disables
        this.  'textwidth' is set to 0 when the 'paste' option is set.  When
        'textwidth' is zero, 'wrapmargin' may be used.  See also
        'formatoptions' and |ins-textwidth|.
        When 'formatexpr' is set it will be used to break the line.
        NOTE: This option is set to 0 when 'compatible' is set.


'wrapmargin' 'wm'       number  (default 0) 
                        local to buffer
        Number of characters from the right window border where wrapping
        starts.  When typing text beyond this limit, an <EOL> will be inserted
        and inserting continues on the next line.
        Options that add a margin, such as 'number' and 'foldcolumn', cause
        the text width to be further reduced.  This is Vi compatible.
        When 'textwidth' is non-zero, this option is not used. 
        See also 'formatoptions' and |ins-textwidth|.  {Vi: works differently
        and less usefully}

Reference:

http://stackoverflow.com/questions/1290285/why-cant-i-stop-vim-from-wrapping-my-code
http://stackoverflow.com/questions/15724919/how-do-i-prevent-vim-from-auto-wrapping-at-column-80