Search string length

[malum]

This seems to be set at 20 characters
I thought I had found out where this setting is (SCRIPT_search.php)

but changing the value doesn't seem to enable a longer search string

This is what I have put (it was 20) but it hasn't made any difference. Anyone know how to do it?

ob_start();
        if ($search_row != $q45) {
            ?><input type="text" name="keyword" value="<?php print ee_html_conversion($keyword); ?>" size="25" maxlength="255" class="ee_css_keyword_input" /><?php
        }
    $form_search_keywordfield_html = ob_get_contents();
    ob_end_clean();