Educate me on why 340 fan is not symmetrical

Three reasons. It moves more air, it's quieter doing it and there's less drag than a symmetrical fan because of how it breaks the air up. The MP engine book has covered all this in good detail for close to fifty years. The problem there is also three fold. First, people refuse to believe what they read. Secondly, people won't read what you tell them. Lastly, now, unfortunately, the MP engine book is getting difficult to find copies of. I think the last printing was the ninth edition for both the engine and suspension manuals. I used to preach those manuals hot and heavy around here, but I just gave up for the three reasons mentioned above. Especially the first reason. People just will not believe the information in those manuals. They'll argue every step of the way the information is "wrong" as if they somehow know more than all of the racers and engineers whose vast knowledge spans well over 100 years collectively.