Pops, bangs and crackles

[Cfnteabag]

I was thinking today what is it that causes an exhaust to pop and crackle etc on the overrun? I was under the impression it was unburnt fuel hitting the hot exhaust but how can that be on a modern car with cats?

I love the sound of a car popping and banging, makes me think about rallying from the mid nineties backwards, now I'm fairly sure that was because of the turbo

[Buff Mchugelarge]

Was thinking much the same the other day.

The TVR Chimera I was following was popping away where my De'cat'd (?) Mx5 won't have any of it?

I'm thinking a stainless exhaust manifold may help?

[Troubleatmill]

Mine does it all the time. Part of its charm.

[TheEnd]

It's the other way around, and it's air getting to the cats and burning the traces of fuel that has collected.

[Spoof]

Fueling and valve overlap I guess.

[Mastodon2]

Manifold is not really important, neither is the cat. The fuelling map of the car has more to do with it; My Type R pops and crackles on gear shifts, occasionally lets out a loud, sharp crack from a big gout of fuel flashing off in the pipe, the car is running a straight-through exhaust from the catback. A friend had a Fiesta ST, and he added a straight through catback and the pops and bangs were unreal, every time he took his foot on the throttle it would snap and bang like crazy, much, much more than Civic. It was quite comical and sounded like a Chinese firework factory on fire, but in the end it was too much for him so he put a restrictive Milltek exhaust on that strangled the noise. The STs do seem to have a real penchant for banging, as I've seen a few with suitably de-restricted exhausts, on standard manifolds and cats, and they all banged away like mad too.

There are tuning companies who offer "pops and bangs" as part of their remap functions for Imprezas and RS Clios, by turning up the fuelling on an unburnt thread or altering the spark retard or something, so more unburnt fuel gets into the exhaust to flash off.

[AndyBrew]

981 Boxster S with PSE does this for fun every lift off the throttle releases a chorus of pops!

[Cfnteabag]

So if I was to add a straight through cat back exhaust to my puma I may get the same effect?

[Mastodon2]

Cfnteabag said:

So if I was to add a straight through cat back exhaust to my puma I may get the same effect?

Depends, some cars don't seem to mind the cat being in and will pop and bang like crazy, others can have really loud exhausts (as a result of not having any silencers in place) and still don't really pop and bang. A decat and a suitable exhaust would be a surefire way to get pops and bangs if that is what you are after.

http://www.youtube.com/watch?v=J-e70GArPfI

Above is a video of someone who has altered the limit of their hardcut rev limiter to 4000rpm, so when the car hits that limit it prevents the fuel from igniting, dumping it in the exhaust, causing the loud bangs, which proves a Puma 1.7 can bang. Your car would be somewhere between loud and really fking loud if you put a straight through on though, they aren't for everyone, shrinking violets need not apply.

[s p a c e m a n]

Unburnt fuel in the exhaust helps, heres a cheap diy solution that I have just remembered about http://www.youtube.com/watch?v=vEashMzvifg

[JDMDrifter]

http://m.youtube.com/watch?v=VkEWadB0ScI

A little vid of my golf , it's only got the center silencer left after I replaced the back box with a stainless pipe. This pop and crackles on overrun due to the carb dumping fuel !

[vxr1]

My insignia does it, at low speeds when I let go of the accelerator it crackles and it bangs quite loud when I accelerate fast and change up a gear.

[Mymk5zs123]

Cfnteabag said:

So if I was to add a straight through cat back exhaust to my puma I may get the same effect?

I think you need a tape ecu and 4-2-1 manifold to make a puma pop like crazy.

[David87]

It seems to be something that's easy to engineer into the electronics nowadays - my R56 MINI Cooper S is silent with the sport button off, but with it on it pops and bangs in a way you wouldn't expect from a little girls' car.

[giggity]

s p a c e m a n said:

Unburnt fuel in the exhaust helps, heres a cheap diy solution that I have just remembered about http://www.youtube.com/watch?v=vEashMzvifg

Excellent

[Raize]

Unburned fuel for whatever reason. Caused by lean mixture OR rich mixture - lean because lean mixtures take longer to burn, and if the mixture is over-lean for the timing then it will not finish it's combustion before it is exhausted. Rich mix is a more common cause here though, simply dumping too much fuel into the cylinders causes unburnt fuel to be exhausted. Pops and bangs from rich mix are likely to be a side effect of being tuned for power (by using too much fuel), but pops and bangs from lean mix would be more likely a fault.

[Ozzie Osmond]

"Sports exhaust" is IMO exactly the same as sticking a piece of cardboard in your bicycle spokes. In other words, strictly for kids.

Serious drivers can usually press the throttle pedal to achieve suitable results.

[Spoof]

Ozzie Osmond said:

"Sports exhaust" is IMO exactly the same as sticking a piece of cardboard in your bicycle spokes. In other words, strictly for kids.

Serious drivers can usually press the throttle pedal to achieve suitable results.

What now?

[Motorrad]

Ozzie Osmond said:

"Sports exhaust" is IMO exactly the same as sticking a piece of cardboard in your bicycle spokes. In other words, strictly for kids.

Serious drivers can usually press the throttle pedal to achieve suitable results.

Nah-the right one will provide a performance benefit. Or failing that remove overly restrictive factory sound deadening that stops you hearing the lovely noise of your V8 properly and sharing it with everyone else........

[V88Dicky]

DFCO causes (most of) the pops and bangs on a Monaro.



Deceleration Fuel Cut Off