[RenatoMN]

Try it:

AdminCP > Plugins > Add a Plugin

Product: vBulletin
Hook: postbit_display_complete
Title: Replace thread title
Execution order: 5

PHP Code:

$post[message] = str_ireplace("{title}","$foruminfo[title]",$post[message]); 


Plugin is active: Yes //do not forget this

(you may see a line break here, but it's all a single line)

note: str_ireplace (case insensitive) is a bit more intensive than str_replace.
Use str_replace if you prefer (your users will forced to use it in lowecase).