I have 2010 f150 supercrew 4x4 6.5ft box 5.4l. The exhaust that comes off of the manifolds is 3 inch in diameter. Then there is another pipe that is 14 inches long that is 2 1/4 inches in diameter and then that pipe goes onto another pipe that is 2 1/2 inches. My question is why the 2 1/4 pipe is used. I don't know why they just didn't use 2 1/2.