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Catalytic converter Pipe

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I've looked this up on multiple forums and haven't been able to get ONE consistent answer to this question which I thought would've been fairly easy to find. I'm looking to make a custom exhaust for my 97 540 and I want to install an X pipe right after the O2 sensors but I want it to clamp on so I can access the driveshaft if needed. I know the factory exhaust clamps on at that same position and realoem says those clamps are 55mm which is 2.165", so is the exhaust pipe coming from the cat 2" and the piping going to the rest of the exhaust slightly larger or is exhaust coming from the cat 2.165" and the exhaust clamped to it smaller? Or are they both the same and butt connected. I ask because I'm sure you all know but there aren't exactly a variety of options at 55mm for exhaust components.
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Get thee to an exhaust system specialist. They will sort it out, and have the correct tools and hardware to effect a clean installation.
That's definitely an option on the list but I was hoping to be able to do some of it on my own, just don't want to buy anything until I have all my sizes correct. Im almost certain I'll need a 2" diameter x pipe either way, just not sure if I'll need a pipe expander to get it over the factory pipe. Realistically everything I have pretty much mapped out just need diameter to determine if it'll work.
Get thee to an exhaust system specialist. They will sort it out, and have the correct tools and hardware to effect a clean installation.
You can measure the outer circumference (C) of the pipe with a tape measure. Then use the formula d = C/pi, where d is the OD of the pipe, and pi = 3.14

Use a tailor's tape for the most accurate measurement.
Not the answer I was looking for however it may be the most accurate, I'll try it.
You can measure the outer circumference (C) of the pipe with a tape measure. Then use the formula d = C/pi, where d is the OD of the pipe, and pi = 3.14

Use a tailor's tape for the most accurate measurement.
What answer WERE you looking to get?
I was hoping someone knew the answer off the top of their head. I kind of figured it wasn't the most common of knowledge but maybe I'd get lucky and someone would know for sure and reply.
What answer WERE you looking to get?
Eventually someone may have the answer but if you can't wait, use the formula. Probably quicker anyway in a more purist oriented sub forum.
Yea I'll probably do it this week, I have to do my cv boots anyways so I'll be down there.
Eventually someone may have the answer but if you can't wait, use the formula. Probably quicker anyway in a more purist oriented sub forum.
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