Increase number of characters in my rss feed

How can i increase the numbers of words (characters) inside my rss feed?

Here is an exemple this post :
http://www.tvqc.com/2011/03/spartacus-blood-and-sand-qui-sera-de-la-prochaine-saison/
Title: Spartacus Blood and Sand: qui sera de la prochaine saison.

the excerpts is
Les fans de Spartacus n’ont désormais p […]

id like to increase this line to give at list the 2 first line.