.site,
.site-header {
 max-width: 100%;
}

add_filter('twentfourteen_header_image_height','my_header_height');
add_filter('twentyfourteen_header_image_width','my_header_width');
function my_header_height($size){
   return 100;
}
function my_header_width($size){
   return 1000;
}

/*This section sets page to 100% width */
.site {
	background-color: #fff;
	max-width: 300%;
	position: relative;
}
/*This section sets page header to 100% width */
.site-header {
	background-color: #000;
	max-width: 100%;
	position: relative;
	width: 100%;
	z-index: 4;
}