Dear Alejandra,
please clarify – do you want the titles to be hidden on pages with the “Portfolio” template – or on the portfolio projects (i.e. the pages you get to when you click any of the portfolio boxes)? If the former, then the Theme Options setting “Hide page titles on pages” (“Page Elements” tab) should do the trick. In case you meant the latter, the Theme Options setting mentioned above will not affect them, since they are not pages but posts (of type “Project”); in this case you can use the following CSS:
.single-project .post-header { display: none; }
Please let me know if I misunderstood the question!
Sincerely,
Andrew / Satori Studio