I believe when reading Hassan's exhaust journey thread on the old m3forum that upsizing the stock section 1 from 2.16" (I think) diameter to this 2.5" diameter yielded tq improvement (maybe 5-8) when paired with catless headers on his friends car.
Manzo makes a 2.5" straight pipe for $135. And you're free to weld in one or two AR25's. That being said when I did this, I noticed a decrease in exhaust pitch and rasp. I for one enjoy the higher raspier pitch and so I've since switched back to the stock section 1. Ultimately I'm happy to sacrifice a few hp here, and few tq there, for my subjective satisfaction with my exhaust note.
Also, I think there's better ways to spend $600 on our cars anyway. If rasp removal is ur motive, welding in an AR20 is my suggestion.
Manzo makes a 2.5" straight pipe for $135. And you're free to weld in one or two AR25's. That being said when I did this, I noticed a decrease in exhaust pitch and rasp. I for one enjoy the higher raspier pitch and so I've since switched back to the stock section 1. Ultimately I'm happy to sacrifice a few hp here, and few tq there, for my subjective satisfaction with my exhaust note.
Also, I think there's better ways to spend $600 on our cars anyway. If rasp removal is ur motive, welding in an AR20 is my suggestion.
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