Pops, bangs and the cat on new cars?

[feef]

I was listening to the burble on the overrun on my supercharged MX5, and was contemplating the noises we hear from some new cars where the rice crispies effect on the overrun is quite deliberate.

Now correct me if I'm wrong but those pops and bangs are caused by unburnt fuel entering the exhaust, however from my experience (with a blown coil pack and a misfire) unburnt fuel in the exhaust is a bad thing when it comes to catalytic convertors.

So it makes me wonder, are these cars doing something interesting with the cat or exhaust flow to allow these noises without damaging the cat? Or is cat life acceptably shorter as a result?

[Ozzie Osmond]

feef said:

caused by unburnt fuel entering the exhaust

I think they do it other ways these days, in view of economy and emissions.

[DS197]

It could just be that the engines are highly tuned which makes them more susceptible to pop and bang. I mean if you look at the typical hot hatches with a n/a 2 litre engine, it doesn't take much for them to make some noise. My Clio is significantly more vocal by just removing the centre silencer. I guess newer cars with active exhaust technology make a difference too? But to answer your question, I don't think the life of the cat is severely reduced unless the car is over fuelling like mad.

[Richyvrlimited]

Burbles are tuned into overrun conditions by having a lean mixture and pretty retarded timing. it's not unburnt fuel per-say causing the noise, it's combustion continuing into the exhaust rather than all happening in the combustion chamber.

I doubt it'll have any real long term effect on a CAT.

Now bangs are unburnt rich mixtures igniting on hot parts of the exhaust. Those will kill a CAT, (and exhaust baffles) PDQ.

[nunpuncher]

The popping and banging is getting a bit ridiculous. People seem to be obsessed with it. The F-types sound ridiculously shouty and i find the forced "parps" on upshift on the A45 and the Golf R irritating.

[Martin_Hx]

I saw a video the other week of that A45 with the banging/popping, it was bloody awful! I wonder if theres a button to turn them off?

[anonymous-user]

Worth noting that a lot of the exhaust theatrics are a result of the heavy spark retard required for a DSG transmission (or modern auto) to change gear without the associated lag of shutting the throttle (and having to wait for the airflow to build again) In effect, the mean exhaust gas Lambda is still close to stoiciometric, but the burn event occurs partially in the exhaust manifold, hence flywheel torque is massively reduced. Although this does lead to elevated exhaust line component temps, for the short duration of an upshift it is containable.

It also has less effect on tailpipe emissions as the catalysts oxygen storage is not adversely affected (unlike cutting the fuelling into overrun fuel shut off, and the resulting lean spike and uncontrollable mid brick exotherm if entered from a fuel rich state)

[klunkT5]

Anti-Lag

[ChrisRS6]

Latest RS6 sounds epic!

[irfan1712]

I think the F Type and Range Rover SVR are massive culprits. Surely must get a bit boring after a few hundred miles?!

[Megaflow]

They are getting a bit out of hand, I was following a new MX5 the other day, it was about 4 cars in front of me and I could hear it over the exhaust in my S1 Elise.

At first I thought my exhaust had gone...

[feef]

Martin_Hx said:

I saw a video the other week of that A45 with the banging/popping, it was bloody awful! I wonder if theres a button to turn them off?

I had to look that up.

It just sounds broken


https://www.youtube.com/watch?v=g5J6W9Y6hUU

[blearyeyedboy]

It sounds strange, like when I was a kid and used to cut a bit of a Weetabix packet out and clip it to my bicycle wheel to make a buzzing noise.

Just me then?

[shielsy]

Secondary Air Injection... used to clean up emissions by injecting air into the exhaust to allow combustion of gases. A side effect is popping and banging on overrun.

[csd19]

shielsy said:

Secondary Air Injection... used to clean up emissions by injecting air into the exhaust to allow combustion of gases. A side effect is popping and banging on overrun.

Usually only runs during a cold start though? Helps with getting the cat up to operating temperature more quickly.

[R8VXF]

feef said:

Martin_Hx said:

I saw a video the other week of that A45 with the banging/popping, it was bloody awful! I wonder if theres a button to turn them off?

I had to look that up.

It just sounds broken


https://www.youtube.com/watch?v=g5J6W9Y6hUU

Oh dear god, those upshifts sound horrendous!

[Dannbodge]

That AMG sounds stupid.

Pops and Bangs on the overrun are okay but going up through the gears? not for me thanks

[R8VXF]

I guess it is to do with the anti-lag, but just sounds like someone is stepping on bubble wrap every time he shifts.

[Ved]

Sounds awful and synthetic. Nothing that Audi hasn't been doing on their S and RS cars though.

[0000]

Surely that's broken?