Look at the photo of the Mosquito on this page. On each engine, you can see the exhaust stubs. Those are ejector stacks. If you launch AH and grab a Mosquito and look at its engines, you will see that area of the engine cowling is covered up, under it would be a device that resembles a saxophone that cools the exhaust gasses and prevents the flare from being visible.
On aircraft with ejector stacks they can receive up to about 10% of the engines power as thrust due to the exhaust gasses being directed.
For example, the only powerplant change from a 332mph A6M3 Zero to a 350mph A6M5 Zero is the addition of ejector stacks to direct the exhaust to the rear, causing forward thrust.