Why does a car exhaust "crackle" on deceleration?

Emission · Emission's Garage

My 930 makes a really cool "crackle" on deceleration/downshifts. It has always done this. Now, with a new exhaust and no CAT, it really is pronounced (I'm not complaining - it brings tears to my eyes it sounds so good!).

What causes it? Is it harmful?

sammyg2 · 05-13-2005, 09:00 AM

LOL welcome to my world, at least until recently.
My engine did the same thing ever since I bought it, gurgled and popped out the exhaust on decell.
It did it before the turbo was installed and after.
I tried everything I could think of to get rid of it, nothing helped. When I say everything, I mean everything. From checking pressures to checking every single component, I did it. Even a top end overhaul (broken head stud).
Finally, I replaced the O2 connector that hooked the O2 sensor to the wiring harness. Bingo, it went away. The car ran smoother, idled smoother, and the gurgle was almsot completely gone. My exhaust is a tad louder than stock so I can still hear a slight noise, but only if I really listen for it and even then it is still one of those things that I think I can hear but not sure.
I have no idea if your problem is the same as mine but that is what worked for me. Inspect the wiring and connector real close, and if in doubt, replace it.

Emission · Emission's Garage

My O2 sensor is new (from my smog test fiasco about six months ago). My idle is smooth, and my fuel consumption is normal.

Is it because my engine is running rich (deliberate)?

I thought it was a "mini backfire" from unburned fuel igniting in the hot exhaust... but the engine does it ice cold too!

It doesn't sound like it is hurting anything.

Az911 · 05-13-2005, 09:09 AM

The more open the exhaust the more "crackle". Listen to a Harley with straight pips is crackles like no tomorrow

JackT · 05-13-2005, 10:04 AM

I love the crackle sound. I have lost it since putting SSI's and a Dansk on my car.

t.brady · 05-13-2005, 10:08 AM

emission -- what type of exhaust did you go with?

Emission · Emission's Garage

I went with the Fabspeed dual. I'll post installed pics on Monday once my valance is back on (I am cutting, stripping and painting it).

The Fabspeed is a true "dual" exhaust - one pipe (the right) is for engine exhaust and the other (left) is a wastegate dump pipe. Both are completely separate, just like the 964 3.6 Turbo's factory exhaust. I looked at others, but I didn't like how they had one pipe into a muffler, then two pipes out (giving the "appearance" of a dual exhaust). The Fabspeed is one 3" in, and one 3" out.

I'll post pics in a couple days.

nixter · 05-13-2005, 10:34 AM

I have the same thing but opposite. It was silent when my car was running rich and my fuel milage sucked. Now it's leaned out and I get crazy crackling. I have no o2 sensor however.

Nik.

Rick Lee · Rick Lee's Garage

I'm running SSI's and a dual in/out B&B with O2 unplugged. My car gets super gas mileage and it gurgles like crazy and very loudly so. I'm a little worried. Is it normal?

}{arlequin · }{arlequin's Garage

i always like a good gurgle....

with Ben's muffler, it's better than ever

porschenut · 05-13-2005, 11:17 AM

I want crackle! How do I get it?

Steve87-911 · Steve87-911's Garage

I think it's inherent in free flow exhaust systems. Mine's not really a crackle, more of a minor futt futt futt on decel.
Anyway, you should be accelerating instead so you can hear the real music.

Craig 930 RS · 05-13-2005, 11:27 AM

But,,,,,,WHY does it crackle?

My 1997 3.6 engine crackles and pops like crazy......I love it

Mysterytrain · 05-13-2005, 11:27 AM

Funny you should say that..I've got SSI's and a Dansk 2 in 1 out and I'm not in love with the sound of the Dansk.

trader220 · 05-13-2005, 11:54 AM

I am by no means an expert but I have a lot of experience with HD motors. The way I understand that phenominum in the HD motors with straight pipes is that there is very little back pressure and what you here is actually the motor sucking air back up the pipe between strokes. Again, that’s what I have been told and I DON’T swear by it. The less back pressure (i.e. more free flowing the exhaust is the greater the crackle)

t.brady · 05-13-2005, 12:14 PM

emission, thanks. i will most likely go with the fabspeed dual. i'm also considering welding the factory tips onto a single out ghl. what type of headers are you running?

}{arlequin · }{arlequin's Garage

i don't know anything about the "why" but it sure is fun to let the revs drop and crackle/pop while approaching a red light, especially if i'm in the center lane of a 3-lane road

Rick Lee · Rick Lee's Garage

My car sounds more like a machine gun on decel. It's ridiculously loud. When coming up with a concrete divider on my left, it's even worse.

Emission · Emission's Garage

Quote:

Originally posted by t.brady
emission, thanks. i will most likely go with the fabspeed dual. i'm also considering welding the factory tips onto a single out ghl. what type of headers are you running?

Stock headers (for now).

Emission · Emission's Garage

Quote:

Originally posted by Rick Lee
My car sounds more like a machine gun on decel. It's ridiculously loud. When coming up with a concrete divider on my left, it's even worse.

Mine is also very loud, and more of a really, really, deep "howitzer" boom, boom, boom... "don't even think of messing with me"... sound. It sounds mean.

I like it.

The air going back up explanation sounds most logical.