For torpedoes it is the Torpedoes_US.zon file. The MinEF and MaxEF entries affect the explosive power of the torpedo. The MinRadius and MaxRadius affect the area of the explosion.
For shells it is the same thing, but in the Shells.zon file. See this thread to download a tweak file for it:
http://www.subsim.com/radioroom/show...ells.zon+tweak
There is currently no link for the additional Torpedoes_US.zon file, so I have put the contents into the thread listed below, so you can cut and paste the contents into your own text file.
http://www.subsim.com/radioroom/show...d=1#post534957