[JoeRogan]

I'm planning on doing the muffler delete but I want to know before going to a shop what the diameter of the stock exhaust is, so that I can buy my own tip online first. I can't seem to find this info anywhere, anyone know? I've searched a few forums (one night say exhaustively) and somehow no one seems to have needed to know this before lol

[SDemetris]

go under your car and measure? umm are you talking when its 1 or 2 pipes btw? i think after the resonator its 2.5".. it might be 2.25" though so definitely double check

[JoeRogan]

I would just measure it but it's not like I have verniers I can do it with, and holding up a ruler I feel like I'm just eyeballing it because the pipe will curve away so I could easily be off 1/4". I'm talking about the last section before the muffler under the bumper, I assume that's the one that's removed on the muffler delete

[Rival]

2.25 for the most part.

[JoeRogan]

It's 2.5". I found out when I went to an exhaust shop to have the muffler cut off last Saturday

[rattmobbins]

Good to know, thanks!

[N0OS3]

Here is the layout from head-to-toe (literally).... output diameters in (). This is for 325i, 328i, and 330i (n52 engine)... (N54 is considerably different)
Engine (x6 1.5")---> Headers with catalytic converters(x2 2.25") ---> secondary catalytic converters (x2 2.25")---> resonator (x1 2.75")--->muffler (x2 2.25")

[Hotter]

It seems that there are different variations.

This is my measurements of E92 328i 2010 (maybe its useful for anyone):
Engine (x6 ?) ---> Headers with catalytic converters (x1 ~52mm 2.05" x1 ~55mm 2.15") ---> secondary catalytic converters (x2 ~55mm 2.15") ---> resonator (x1 65mm 2.55") ---> muffler (x2 ?)

Share you measurements and model to see the differences. I would like to know all variations and differences.

[stilesg57]

Been down this rabbit hole a bit lately too as I debate doing any exhaust work to my car. I've learned more about flow rates required for power at inches of water or inches or mercury or phases of the moon than I ever wanted to.

In the course of that research I found this hand-drawn diagram and saved it, I forgot from whom, but pretty sure it was measurements of a set of AFE catless midpipes, a custom-piped reso delete, and a 328i rear section. Interesting changes in diameter throughout this setup: