After finding this discussion and trying to remember how it was done, I started up Silent 3ditor and looked at Webster's Improved GE Torpedo for SH4v1.5. He adjusted the data\Library\Torpedo.zon "MinEF" and "MaxEF" values, not the .sim "impulse" values...he provided three options; 25%, 35% and 50% increases....and they seem to work quite well.
Next, I looked at the Torpedo.zon values in my stock SH3 and in my GWX3 Gold. In both, the "MinEF" and "MaxEF" values are below the 25% increase values that Webster applied in his aforementioned SH4v1.5 mod. In fact, those values in GWX3 Gold are less than the values in the stock game and the "MinRadius" and "MaxRadius" values are also reduced compared to the stock game's values.
So, if I was going to use an approach that seems to be "tried and true", I'd adjust the Torpedo.zon values back to what they were in the stock game or would even tweak 'em to match what Webster used in his Mod.
Yes, "good hunting" is likely to be easier with a bigger gun!
The Torpedo.sim "impulse" value does nothing to affect the damage caused by the torpedo. According to the folks who were studying and looking for ways to fix the torpedoes in the early days of SH3, the "impulse" is the force/acceleration applied to the target ship model, which causes the ship to shake and/or be lifted up by the "explosion" of the torpedo. Ironically, the problem they were trying to solve was the massive damage caused, often breaking even large ships in two and/or obliterating them with a single hit.