Ejector stacks increase horsepower

When you come from a company known for building racing planes, you learn to steal any advantage you can get. Supermarine’s Spitfire (and Hawker’s Hurricane, too) have ejector stacks on either side of its Merlin engine that help exhaust escape, not to the sides, but almost directly aft. Though testing was limited, the push from the plane’s high-speed exhaust gasses was reported to have amounted to 70 additional horsepower, raising top speed by as much as 10 miles-per-hour.