i'v tried to create a spitfire engine sound as close a s possible to a Merlin Engine sound. I think it's quiet difficult to make a Merlin Engine sound but i tried my best on it.
all my respect to Mitsu who made a great job with his sound files. It took me days to make that one.
Try it out by "right click" for download. Dont forget to make a backup of your original "eng.wav" file.
http://www.me109.net/sounds/eng.wavairmess