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      03-06-2019, 09:08 AM   #9
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Drives: 2013 328i xDrive
Join Date: Jun 2017
Location: New Jersey

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Originally Posted by CandyRedRC46 View Post
I will preface this by agreeing with Mike... My AFE down pipe fitment sucked in original form (more on that in a bit).

All down pipes taper down to 2.25" inner diameter. It doesn't matter if its a $99 ching chong ebay special or a $1000 AR/ER/Wagner etc. It doesn't matter if the company that sold it to you advertised it as a 4" downpipe. They all neck down to a 2.25" in dia exit, in order to slip into the factory catback exhaust. The same goes for all cat back exhausts and front pipes. They will all neck down to about a 2.45" inner diameter at the entrance, in order to slip over the factory down pipe....

For some reason none of you people (BMW owners, Vendors or Tuners) seem to care lol. I have had countless people tell me that a couple inch long section of 2.25" piping isn't a big deal and it won't effect performance, but I am an engineer and studied Fluid dynamics way too much for that not to bother me...

So I installed an AFE catless down pipe and a Supersprint 3" front pipe, cut the 2.25" section out and welded in a 3" flex pipe and 3" V-band. Now it flows and fits better than any of the most expensive name brands could ever dream of.

[puts on flame suit. drops mic. end rant. im out]
Ha I hear you. So of all people I'd think you would agree with me lol. The AR DP not only tapers at exit like you said, but also right before the flex joint, and it looks pretty severe. None of that, including the exit taper to 2.25" will affect performance, but just like I said and like I think you're insinuating, it's can't hurt to have it NOT taper as opposed to having it taper. As mentioned, the preference is unsubstantiated performance wise, but it's a preference I think we both have regardless.
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