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What exactly determined if the exhaust crackles when slowing down and shifting to 1st?

beetle6986

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Ya know, understanding the pops & crackles, it's surprising that damage isn't done to the exhaust system.

But cars have done this for many decades now, so I suppose it's all good.
I think it depends on whether the car does it naturally or it is introduced with a tune. My Cobra crackles a lot naturally on decel. The crackle tune in the BMW is ridiculous. It doesn't sound natural at all. It's almost like explosions in the exhaust system. Sounds really bad in IMO.
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engineermike

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You can turn DFCO off in the cal and a/f will stay at stoich on decel and it will do it more. You can also adjust the spark decel torque authority to increase or decrease it. And finally, the Ford cals have a “burble mode” option that I think is similar to the bmw thing. However, I haven’t run across a cal yet where it was activated.
 

m3incorp

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The manuals on stock exhausts are the same. Add an aftermarket exhaust and it changes big time. Mine crackles and pops a lot.
 

NoVaGT

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I think it depends on whether the car does it naturally or it is introduced with a tune. My Cobra crackles a lot naturally on decel. The crackle tune in the BMW is ridiculous. It doesn't sound natural at all. It's almost like explosions in the exhaust system. Sounds really bad in IMO.
I'd think that there's a cumulative effect on the health of the exhaust system. Over time, pops and crackles (small explosions) in the exhaust system will eventually blow out baffles and such.

But since most people that want the pops and crackles install exhaust systems with little to no baffles, it's not really a concern.
 

beetle6986

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You can turn DFCO off in the cal and a/f will stay at stoich on decel and it will do it more. You can also adjust the spark decel torque authority to increase or decrease it. And finally, the Ford cals have a “burble mode” option that I think is similar to the bmw thing. However, I haven’t run across a cal yet where it was activated.
That's what they call it! "burble". I couldn't think of it.


The manuals on stock exhausts are the same. Add an aftermarket exhaust and it changes big time. Mine crackles and pops a lot.
My Cobra didn't do it at all with stock exhaust. It started crackling pretty good once I added a Borla catback and Bassani mid pipes.
 

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Zooks527

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My Cobra crackles a lot naturally on decel.
Well, "naturally" is a misnomer. Ford has the system setup to produce the pops and crackles because that's what people want - a car that sounds like an older carbureted engine. They're dialed in from the factory. If Ford desired, there wouldn't be any.
 

FrankM5

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Hmm i have had a different experience on MY19 GT when i was full catback i wouldnt get any burbles or ever slight but adding the resonator back and only having my mufflers it cracks more but it only ever cracks when im in Manual mode (10Speed) and playing with the paddle's and i could only get it to pop on 3rd gear around 4500 rmp any thoughts or suggestions. Also it doesnt matter on what "Mode" im in they all crack and pop the same way
 

dx2

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Since the weather allowed some driving today I could consistently get it while the car was already warmed up, in normal mode, no rev matching while shifting down into 3rd.
 

Jimmy Dean

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um, normally popping in the exhaust on deccel is because it is too lean, not enough fuel for the RPMs. this is why performance builds do it most often, because they cut fuel on deccel to help with engine braking, reduce wear and heat on the brakes.
 

Kong76

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As far as a manual, I don't have rev match but I never downshift into first ever. I use that gear for take off only.
 

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FrankM5

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um, normally popping in the exhaust on deccel is because it is too lean, not enough fuel for the RPMs. this is why performance builds do it most often, because they cut fuel on deccel to help with engine braking, reduce wear and heat on the brakes.
So my car is running normal thats why it doesnt pop on deccel?
 

Jimmy Dean

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So my car is running normal thats why it doesnt pop on deccel?
well if it doesn't pop, it is running more normal. there are a couple of ways to fix the popping, either get the correct fuel mixture into the deceleration fuel tables, but with an open enough aftermarket exhaust this doesn't always fix it completely, or b) completely cut off fuel (hence the DFCO) as said above, if there is no fuel, there is no pop, but you may get 1 or two quick ones right after you let off the throttle, but it won't continue all the way down as the engine revs drops. on my 351W truck, I had to increase the fuel a bit to get it to go away, it was running lean on decel, which was heating up the exhaust, and any unburnt fuel (there is always some inefficiency) was lighting in the headers. I couldn't cut fuel completely, the engine was deceling too fast

course, running too rich can cause it too, say, on a old V-twin bike, they tend to be setup rich with a big open exhaust that allows fresh oxygen to mix into the exhaust.
 

ALLSTOCK

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I get the pop sometimes on a down shift. I always smile when I hear it, but its definitely not every time.

I think the important take away is that if your car naturally makes the snap crackle pop sounds it'll be ok. If you get something called like a "burble tune" to artificially create these sounds, it can fuck your shit up. If you get a burble tune I will personally hope for your shit to get fucked up. =)

*edit
theres a pretty good video about it on youtube by alex flores too (the burble tunes)
 

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Once I had a project meeting in the BMW Regensburg plant, all of a sudden we heard this burble/pop sound coming from outside and it lasted for about 2 minutes without a pause and my colleague thought they were manufacturing broken cars :) (he didn't know it was intentionally)
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