Portfolio template get category

Hi all,

Im trying to make a portfolio template that displays only one category of the portfolio.
Currently my portfolio displays all categories and I want it to be one specific category. Any thoughts about how to do that?

the code I currently have is:

function filterable_portfolio_do_loop() { ?>

    <header id="page-heading" class="entry-header">
        <?php $terms = get_terms( 'portfolio_category' ); ?>
    </header><!-- /page-heading -->

    <div class="entry-content" itemprop="text">
         <?php $wpex_port_query = new WP_Query(
            array(
                'post_type' => 'portfolio',
                'showposts' => '-1',
                'no_found_rows' => true,
            )
        );
        if( $wpex_port_query->posts ) { ?>
            <div id="portfolio-wrap" class="clearfix filterable-portfolio">
                <div class="portfolio-content">
                    <?php while ( $wpex_port_query->have_posts() ) : $wpex_port_query->the_post(); ?>
                        <?php $wpex_count++; ?>
                        <?php if ( has_post_thumbnail($post->ID) ) { ?>
                            <article class="portfolio-item col-<?php echo $wpex_count; ?> <?php if( $terms ) foreach ( $terms as $term ) { echo $term->slug .' '; }; ?>">
                                <a href="<?php the_permalink() ?>" rel="bookmark" title="<?php the_title_attribute(); ?>"><?php echo genesis_get_image( array( size => 'portfolio' ) ); ?>
                                <div class="portfolio-overlay"><h3><?php the_title(); ?></h3></div><!-- portfolio-overlay --></a>
                            </article>
                        <?php } ?>
                    <?php endwhile; ?>
                </div><!-- /portfolio-content -->
            </div><!-- /portfolio-wrap -->
        <?php } ?>
        <?php wp_reset_postdata(); ?>
    </div><!-- /entry-content -->

<?php }

genesis();