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2Addicts | BMW 2-Series forum Technical Topics N20 (228i) / B46 (230i) Engine, Transmission, Exhaust, Tuning Modded exhaust "thump" on high-RPM upshift: not complaining, just curious

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      10-08-2015, 12:45 AM   #1
BarryJI
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Modded exhaust "thump" on high-RPM upshift: not complaining, just curious

Since getting a Dinan Freeflow exhaust installed on my 228i 8AT I've noticed a pronounced "thump" (both a sound and a brief percussive sensation) from the underside of the car during high-RPM upshifts. FWIW, the new cat-back exhaust eliminates the factory computer-controlled exhaust valve, according to Dinan. I'm not complaining about this, just curious about what is happening here that didn't happen before and if it's to be expected. It seems completely harmless but if it isn't I would obviously be grateful to know. Finally, how would this sound be perceived from outside the car, if at all? Thanks!
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      10-08-2015, 04:37 AM   #2
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Does it sound like a Volkswagen DSG on the upshift?

If it's a burp when you are shifting at 4-7k rpm it is perfectly normal, in fact a lot of owners find this noise addictive such as myself
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      10-08-2015, 05:38 AM   #3
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A sound clip would be helpful...
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      10-08-2015, 01:52 PM   #4
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Quote:
Originally Posted by AUSf22 View Post
Does it sound like a Volkswagen DSG on the upshift?

If it's a burp when you are shifting at 4-7k rpm it is perfectly normal, in fact a lot of owners find this noise addictive such as myself
I think it's this. It may well be an offshoot of the tune, not the exhaust. Either way, it appears not to be something to worry about. It certainly does not pause the upshift unduly.
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      10-08-2015, 08:14 PM   #5
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Quote:
Originally Posted by BarryJI View Post
Since getting a Dinan Freeflow exhaust installed on my 228i 8AT I've noticed a pronounced "thump" (both a sound and a brief percussive sensation) from the underside of the car during high-RPM upshifts. FWIW, the new cat-back exhaust eliminates the factory computer-controlled exhaust valve, according to Dinan. I'm not complaining about this, just curious about what is happening here that didn't happen before and if it's to be expected. It seems completely harmless but if it isn't I would obviously be grateful to know. Finally, how would this sound be perceived from outside the car, if at all? Thanks!
Mine does that also, does it sound like this?

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      10-08-2015, 08:34 PM   #6
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Kind of. It's a kind of a thud. I don't know what it sounds like from the outside of the car. I will record it when I next have a passenger. To do so alone would not be safe as it happens only during aggressive shifting at between 4k and 7k rpm.
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      10-13-2015, 07:20 PM   #7
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this kinda sound? i love it
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      10-14-2015, 01:03 AM   #8
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Yeah, that may be how it sounds from the outside. I was mistaken to describe it as an exhaust-related sound (although I first heard it after getting a new exhaust). The "thump" may be from the transmission or the drivetrain for all I know. It's certainly an "I'm going fast" sound, it does not appear to slow down the 8AT's very fast upshifts, it occurs only when accelerating pretty aggressively and seems harmless.
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      10-14-2015, 08:47 AM   #9
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Quote:
Originally Posted by BarryJI View Post
Yeah, thast may be how it sounds from the outside. I was mistaken to describe it as an exhaust-related sound (although I first heard it after getting a new exhaust). The "thump" may be from the transmission or the drivetrain for all I know. It's certainly an "I'm going fast" sound, it does not appear to slow down the 8AT's very fast upshifts, it occurs only when accelerating pretty aggressively and seems harmless.
I've heard it's from the transmission too, something to do with fast shifts causing it Some interior clips of mine, if it's at all relevant:



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      10-29-2015, 06:24 PM   #10
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Ive alway attributed at least some of the "percussive" aspect you're on about to the active sound too. The subwoofers are under the seats after all (with HK). However, i do experience more aggressive shifting from time to time with the 8AT in sport + that compounds the effect somewhat and I'm running the stock exhaust atm.
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      10-30-2015, 02:30 PM   #11
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Quote:
Originally Posted by allthatisntnow View Post
Ive alway attributed at least some of the "percussive" aspect you're on about to the active sound too. The subwoofers are under the seats after all (with HK). However, i do experience more aggressive shifting from time to time with the 8AT in sport + that compounds the effect somewhat and I'm running the stock exhaust atm.
Just FYI: ASD only emits from the rear speakers. This has been demonstrated because aftermarket amp installations spike the volume of ASD unless the amp itself has independent gain control for each channel or ASD is coded off. This is the case with Hi-Fi ('base' in the U.S.) or HK.
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