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BMW 3-Series and 4-Series Forum (F30 / F32) | F30POST > Technical Forums > N20, N26, B46, B48 Turbo Engine / Drivetrain / Exhaust Modifications > N26 w/BM3 stage 2 & secondary cat
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      10-15-2019, 08:26 PM   #1
Green33
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N26 w/BM3 stage 2 & secondary cat

Iím wondering if there is any risk/increased wear to my turbo if Iím running BM3 stage 2 with an ER high flow DP but kept the secondary cat and remaining stock exhaust components in place. The DP is 200 cell and secondary cat is 400 cell. This is basically the same restrictions as the factory N20 DP which BM3 says to replace with high flow or catless DP to not wear the turbo on stage 2. Should I be planning a cat delete or because the secondary cat is further down the exhaust it doesnít impact the turbo? Have 20k miles on my car and would like to keep it for another 5 years or so running stage 2 and not planning any more mods.

Any info to prove/disprove my concern is appreciated.

328ix LCI 8AT Sport Line N26 | OCC | VRSF 5" HD FMIC | ER CP | ER Catted DP | BM3 Stage 2 93
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328ix 8AT Sport Line N26 | OCC | VRSF 5" HD FMIC | ER CP | ER Catted DP | BM3 Stage 2 93
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      10-15-2019, 09:08 PM   #2
CandyRedRC46
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Any reason you don't want to delete the secondary cat?
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      10-15-2019, 09:26 PM   #3
Green33
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I just donít want to go down the exhaust mod path. Doing the DP and tune were the best bang for the price mods and keeps the car sounding close to stock.
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      10-15-2019, 10:13 PM   #4
rjdnyy224
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You can run stage 2 with the secondary cat in place. Ideal would obviously be full catless, but if you want to keep that 2nd cat you can.
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      10-15-2019, 10:47 PM   #5
Green33
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Thanks. If I were to go to a custom muffler shop and get the secondary cat deleted any idea of the gains? I donít want to do the full mid pipe as that ends up being $1000CAD plus install. Trying to use math on gains+turbo reliability to cost. Assuming not much gain or increased turbo wear Iím likely to stay as is. I went catted DP so there would be no fuel smell. Not trying to open that debate but I have no smell at all as is.

Last edited by Green33; 10-16-2019 at 08:59 AM..
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      10-16-2019, 03:23 AM   #6
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I'm in the same situation too. I have vrsf downpipe and wanted to delete the secondary cat so I asked what the difference in power gain would be. some people say 5 to 10hp gain but there is no evidence.
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      10-16-2019, 08:10 AM   #7
CandyRedRC46
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dude.... any competent muffler shop can delete the secondary cat for around $50...
You could even weld a resonator in its place for not much more...
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      10-16-2019, 09:10 AM   #8
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Agreed that it would make sense removing the cat would add some HP. Similar logic for high flow cat vs catless DPs. Small difference but still there. Would need a few dyno runs to prove it.

Iíll check on the local boards to see if anyone near me has done a 2nd cat delete and the price.

Thanks for the feedback all.
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      10-21-2019, 12:23 PM   #9
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No risk running stage 2 as long as primary cats have been removed
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