1
general::
Speed up, as in They keep passing us so pour on the coal, Mom! or We can get this issue of the paper out on time if we pour on the coal. This slangy expression originated in aviation in the 1930s but must have been an allusion to the coal-burning engines of trains and ships, since aircraft were never so powered. It has since been transferred to other vehicles and other endeavors.
American Heritage Idioms