afterfire or backfire?
 

I recently had an aftermarket CBE installed (less than 30 days ago) and have recently noticed a muffled backfire/afterfire upon deceleration. I never hear it when I am hitting the throttle, and usually hear it when I let up on the gas to shift gears.

Is this caused by an exhaust leak? is the car running to rich? Is this normal, does anyone else have the same sound?

I contacted the company who I bought the exhaust from (they also did the install) but I haven't heard back from them yet. It's been a few days so I thought I would try to get an opinion from the experts on the forum.

Any help would be greatly appreciated.

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As far as I understand it, it's a backpressure pop. Most cars do it, just some you never hear it until you have the kind of exhaust that makes it audible.

Hey bud, sorry that I haven't gotten back to you. It has been very hectic since we got back from the long weekend. Since you are local and I did the install, I would like to hear it in person if you have time. It is not common but always a possibility that something could of loosened up. As a matter of fact, I will just give you a call right now...

Thanks, Tony

Hey Tony, thanks for getting back to me, I know everyone's busy with the holidays! I may try to swing by after New Years when things aren't so hectic so you can hear what I'm talking about. Like I said, it's not really an alarming sound, just want to make sure it isn't something that I need to worry about.

The noise you are talking about is there stock, just very muffled. I like the noise, it sounds cool. How loud is it?

When I installed TP's a while ago on my 350z it did this every so often. Does this occur frequently or is it a rare occasion?

it's not any louder than the rest of the exhaust note, it just sounds out of place. It goes from a growl to a gurgle back to a growl.

Yeah, it sounds like a normal thing that happens with modified exhausts. It happens on my car every once in a while. You only notice it now that your exhaust is modified and is a little bit louder now.

Yeah, that's totally normal. A little popping and gurgling when you are off throttle... sounds mean. :)

Exactly.

Enjoy the sound...that's my favorite part of any exhaust note. The TopGear guys call it 'runoff'. It's the sweet 'burble' you get when you lift the throttle and decelerate. When I did the muffler delete, it was f'ing awesome.

Heck, when I had my Slowica w/ it's Kazuma exhaust, I got backfires w/ actual visual flame pops. It only happened when hitting on the gas w/ a little load then immediately letting off the gas or pressing in the clutch. Since the car was in the process of accelerating, there was more un-combusted gas in the exhaust that would ignite there.

This is also due to the fact that I was running no cats at the time.

my fc used to shoot flames with racing beat's exhaust because it was running rich and no cats. after getting it tuned no more flames or popping noises.

Ah...The "burble"....Sure wish I had some with the Stillen... I used to love that on my Vette....

HFC's + Takeda intake = lots of burble...

As others have said it sounds perfectly normal. For myself i have the G3 Intakes, with the FI RTP's/18" Res and CF Muffler. To be honest it really is one of the best parts of the sound LOL. Especially accelerating hard in to a tunnel and then just lift off the accelerator. I absolutely LURVE it.

I have the FI TDX CBE 18"resonators w/polished mufflers. The rest of the exhaust sound is so exotic that the burble sounded a bit out of place. It doesn't bother me, however it isn't my favorite sound.

Yes, it is somewhat normal, Berk CBE + Berk HFC gets the burble too. :tup:

My Mini Cooper does it too, check out the video on this one:


A couple links on articles, not sure how accurate they are:

Exhaust Burble Causes | eHow.com

eBay Guides - Exhaust Pipe Diameters

Yeek...More bad info on the internet. I wouldn't put too much stock in either of those 2 links though there is a little truth in the second.

Most cars, due to emissions, now have complete fuel cuts when you close the throttle. This immediate transition to lean will cause the burble and snapping depending on exhaust design and back pressure. On my old ('08) Corvette you could tune this out with software by turning off the fuel cut and allow some fuel and combustibility into the system even on closed throttle. The more even burn did away with the burble and snap/crackle..It was all very tunable. Opening or closing the Exhaust flappers had an impact too.

Race cars burble like crazy. I assume they don't care about emissions though. Is it more exhaust design then?

Anyone getting burble with the Stillen CBE and Berk HFCs together? I have the Stillen CBE alone and there is only a hint of burble.

Here's a good example of the 'burble' at 32 seconds. I think it sounds great.

Yeah I'd love to know what type of exhuast gives you the lift off crackle. I don't necessarily want a louder exhaust but a freer flowing one with over run crackle and pops would be awesome.

I think the mufflers really kill the burble. When I did the muffler delete with stock cats still on the car, the over run crackle was absoluletly awesome. If the WOT acceleration wasn't so darn loud, I'd have kept the muffler delete for the over run burble alone. Man, was it cool.

Ah so the exhaust did get unreasonably loud did it?

http://forums.pelicanparts.com/uploa...1234325242.jpg

yeah i would like that in my car.


what about:
http://markjrebilas.com/blog/wp-cont...ea11y_0344.jpg
I saw a Supra on youtube once pull soemthing along those lines... Don't really care if its not good for the engine, it looks sweet.

My motorcycle does this all the time on decel only. It's normal. I wouldn't worry too much.

I wish my Z gurgled more, its awesome when it does.

Hehe, I used to spit flames out of the STI. Check it out when I brake for the right hander. Lots of chirping BOV, I miss that car. :)

http://www.youtube.com/watch?v=B1TseDZbsrY#t=1m12s

I love the burble of my Invidia Gemini / ERZ combo :yum:

ah man, you'll be carving apexes with that stillen supercharged Z i foresee in your near future:tup:

I have read through the thread but have not seen the answer to the question: what does cause the burble and gurgle? So I'll take a stab: As far as I know, the flames are unburned fuel getting into the exhaust and igniting/burning in the exhaust instead, resulting in popping/burbling noises. This is more present with high powered turbo engines due to running rich and the fact that the turbine housing and wheel get nice and hot and help to ignite the unburnt fuel. I had a friend with a Lotus Esprit turbo, carburetor + turbo= big flames and lots of popping on deceleration. I also once owned a car with a engine with carburetor myself, that car was running rich, lots of popping and burbling. At some point the popping turned into big explosions in the exhaust, getting big enough to blow a hole in the middle muffler :) the muffler just split open like a coke can that had a lit firecracker inserted...

The other reason for burble is air being sucked into the engine, through the exhaust and exhaust valves on deceleration when the throttle is closed. Because there is no ignition and expansion of fuel and air on the 3rd stroke (or power stroke) there will be a slight vacuum in the cylinder when the piston reaches the end of the stroke. So when the exhaust valves open (to let the not present exhaust gasses out), air from the exhaust will be sucked in, resulting in a popping/burbling sound.

This is all AFAIK, please correct me if I'm wrong...

Sounds right JB1, the same burble noise happens with a co-workers Mustang and it is unburned fuel, but once the system warms up it goes away.

I use to have an 07 STi....I do miss that car sometimes. In a perfect world were I had more money I would own my Z and a STi

Interesting that it goes away when the car warms up. With the carburetor cars I referred to it became worse (or better ;) ) when the systems warmed up. Especially the Lotus, that really came alive when warmed up and driven "in anger"...

Bingo.:driving:

Sometimes I wish the Z had more "burble" too. Someone I know owns a r32 with an aftermarket exhaust and it sound awesome.
Kind of like this but not as loud.

Nice Lamo doors... Ah well, guess it's OK as VW owns Lamborghini...

BTW, that's loud... :)