Thread: I gutted my cat
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      05-19-2019, 11:43 AM   #13
XutvJet
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Drives: 2016 M235 6MT
Join Date: Mar 2016
Location: Kansas City

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Beyond the obvious CELs that will now be thrown even with the defoulers, the engineer in me thinks that exhaust flow going from 4" opening tumbling into a ~5" pipe and then out through a 3" pipe is going to impact the exhaust pulses in a negative way. This can impact power delivery, low rpm driveability, and wonky and tinny/farty sounding exhaust noise created within the larger portion of the DP can. With some sort of cats in place, the pressure differential (i.e., backpressure) helps align the exhaust pulses has they go through the varying shaped pipes with little reverberation. The ideal setup would be a graduated straight pipe design like the aftermarket uses.

At least it looks stock and there should still be some power gained assuming the DME doesn't go into some sort of power protective mode when getting odd O2 sensor readings.
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