Quote:
Originally Posted by mike@x-ph.com
Not all downpipes are the same as fitment and air flow play a big role. That being said any proven brand will performance. The only difference is going to be sound.
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Fitment wise you are correct, some cheaper pipes don't Always fit good. But I have seen $1K downpipes have absolute garbage fitment and eBay pipes fit perfectly so pricing is not a factor.
Pricing meaning quality is not a good comparison for the bmw platform especially on an M, because at this point you're talking about M tax on top of bmw tax which is wack and a huge skewing factor. I've seen $200 Subaru downpipes look better in terms of welds and build quality than $1K BMW downpipes.
As long as you don't have crazy bends or a bunch of welding stalactites then airflow shouldn't be impeded too bad, factoring that the diameter is the same.
Sound may be different depending on resonance but I don't suspect it to be too different.