So 2 into 1's are the best for increased performance on stock motors and others, True Duals are next from what I've read in this forum. My question is why does HD go to the expense of using a Y pipe? HD could easily use 2 pipes and at less cost both in materials and labor. I am thinking about just going to rinehart slip-ons and skipping the true duals. So why the Y pipe

 

So HD can maintain the classic dual pipe look and broaden the power curve with the crossover. A true dual system does not give as wide of a power band, itmay show a peak number here or there better but overall average power is down.