I didnt say anything about stacks, but you wont gain anything from them as far as major power, but I like them. a y pipe and duals on a gas truck is the same idea-looks. I understand alot about exhaust ive spent thousands on it. ive owned 15 vehicles in 10 yrs. $ can be spent on better things is my point.
one large pipe will produce more power than a Y pipe

 

Thats what they looked like to me too. It actually kinda peaked my interest (I'm a manufacturing engineer), I'm going to have to look into the fab methods they use.