Originally Posted by Used2be
I don't have experience with turbo motor exhaust, but I have to think that even with the various crimps and compromises in the stock exhaust, the largest obstruction to flow are the cats. When you get the AMS catless downpipes, is there any incentive for IND to test those pipes in an otherwise stock system? I'm sure the larger diameter tube and less restrictive mufflers of the aftermarket manufacturers will give more HP, but it would be interesting to learn the actual HP difference with just the cats eliminated. And I suppose with the cats gone there is the need for adjustment to the ECU, so that would have to come into play as well.
You're correct in saying that the catalysts are the largest restriction of all in the original exhaust system, as well as in saying that any exhaust flow improvement will be best used when coupled with performance software.
I agree that it would be interesting to test the catless downpipes with an OE BMW exhaust, so we'll definitely add that to our to-do list.