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Old 08-16-2019, 05:37 AM   #1
rst.ack
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Join Date: Apr 2019
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Location: Australia
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2015 WRX Premium 6MT

Default Exhaust burbles/pops when rev-match downshifting but not when double-clutching

Bit of an odd question - I have a 2015 WRX that is stock powertrain-wise other than a Nameless catback.

Before installing the exhaust I could hear some subtle burbles when rev-match downshifting. After installing the exhaust the burbles became much more prominent (as expected) and came with some bonus pops every now and again if I downshift just right.

The weird thing I've noticed is that there is no noise if I double-clutch downshift.

Any ideas why this is the case?
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Old 08-16-2019, 06:48 AM   #2
oichan
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2017 Golf-R, etc

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AFR, I believe. Different when repetitive throttle input and release.
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Old 08-16-2019, 08:52 AM   #3
DarkGreyMetallic
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Quote:
Originally Posted by rst.ack View Post
Bit of an odd question - I have a 2015 WRX that is stock powertrain-wise other than a Nameless catback.

Before installing the exhaust I could hear some subtle burbles when rev-match downshifting. After installing the exhaust the burbles became much more prominent (as expected) and came with some bonus pops every now and again if I downshift just right.

The weird thing I've noticed is that there is no noise if I double-clutch downshift.

Any ideas why this is the case?
I've found that revving in neutral on the crackle tune I made doesn't give any pops, but revving in first while stationary does. Crackle tune was made by setting both idle ignition timing tables to negative.

This makes me think there's a different table for idle ignition timing when you're in neutral, so the pops will be different. There's a neutral safety switch so the car knows if you're in neutral or not.

I think stock behaved the same way. I haven't found the 'neutral' table in ATR

Last edited by DarkGreyMetallic; 08-16-2019 at 12:15 PM.
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Old 08-16-2019, 10:17 AM   #4
Schoat333
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The tables adjust based on calculated load.
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Old 08-16-2019, 10:49 AM   #5
jasonwrx86
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The ECU will allow extra fuel in certain conditions.
I notice if you floor the engine in 1st gear to about 5000 rpm and clutch in quick and rev, you will get pops. But if you just randomly rev in neutral, it will not.
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Old 08-16-2019, 01:19 PM   #6
gn4rwhals
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The sound only gets better when you add a downpipe and get loud pops when shifting from the fuel overrun in your tune.

That might just be me though.
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