In a default cart the manufacturer image doesn't have admin-configurable dimensions: it just displays the stored image at it's natural size.
To make the image size controllable from Admin, you'll need to add a couple of configuration keys to the database. Copy the query below and paste it into the box at Admin > Tools > Install SQL Patches, then click the Send button. You'll then have the two new configuration keys available to edit at the bottom of the page at Admin > Configuration > Images.
Code:
INSERT INTO configuration (`configuration_title`, `configuration_key`, `configuration_value`, `configuration_description`, `configuration_group_id`, `sort_order`, `last_modified`, `date_added`, `use_function`, `set_function`) VALUES ('Manufacturer Sidebox Image Width', 'IMAGE_MANUFACTURER_WIDTH', '100', 'Default = 100', 4, 80, NULL, NOW(), NULL, NULL);
INSERT INTO configuration (`configuration_title`, `configuration_key`, `configuration_value`, `configuration_description`, `configuration_group_id`, `sort_order`, `last_modified`, `date_added`, `use_function`, `set_function`) VALUES ('Manufacturer Sidebox Image Height', 'IMAGE_MANUFACTURER_HEIGHT', '80', 'Default = 80', 4, 81, NULL, NOW(), NULL, NULL);
Now you'll have to make an override copy of includes/templates/template_default/sideboxes/tpl_manufacturer_info.php and edit that new file to change this section of code:
Code:
zen_image(DIR_WS_IMAGES . $manufacturer_info_sidebox->fields['manufacturers_image'], $manufacturer_info_sidebox->fields['manufacturers_name'])
to this:
Code:
zen_image(DIR_WS_IMAGES . $manufacturer_info_sidebox->fields['manufacturers_image'], $manufacturer_info_sidebox->fields['manufacturers_name'], IMAGE_MANUFACTURER_WIDTH, IMAGE_MANUFACTURER_HEIGHT)