Vibrant Performance Exhaust

[BMWCurves]

AFAIK the exhaust pipes are 2" OD.

A y-merge to 3" maintains the approximately the same amount of volume that the dual 2-inch pipes provides. Merging to a 2.5" single pipe for the muffler might increase backpressure a bit. I don't have any way to prove this though, lol.

If the stock two pipes are 2" each in diameter, that is ~6.28² inches of cross section (A=pi*r², each pipe is ~3.14² for a total of ~6.28² inches)

The single 2.5" pipe is ~4.91² inches of cross section
The single 3.0" pipe is ~7.07² inches of cross section

I would assume that the single 2.5" would create some back pressure, but I have no background in fluid dynamics for gas so I wouldn't know.