Pops, burbles and growls

[AndyM]

Bit of a school boy question here. I've been mulling over some car related things this evening and came upon a gap in my knowledge regarding exhausts, specifically around the sounds you get from them.

A VXR Corsa came past me on Tuesday (by came past I mean cut me off as I was changing lane) by gunning it up close to the car in the front and then slamming on. Annoyance aside his car did sound surprisingly good and it got me thinking...

As far as I'm aware the pops and burbles you get during overrun on things like touring cars is unburnt fuel igniting in the exhaust. However, my '2 makes none of these sorts of sounds (that I can hear). So, is it just that more powerful cars with bigger flow exhausts and decats purely mean you can hear them better, or, is there something specific that makes them occur in the first place?

Probably a simpletons question but there it is  s:) s:)

[eynonz]

I've heard Toyota Yaris SR with an exhaust that liked a good pop and growl, so don't think it's limited to high powered cars, it was proper loud too (thought a sniper was after me). Mine pops on the odd occasion.

Not sure how people specifically make it do that though, I'm also interested in this.

[mrzwei]

In days gone by that would be down to the valve timing with the engine tuned to be 'on cam' high up the rev range.
The valve overlap would be so great that at anything other than optimum revs fuel and exhaust gasses would be all over the place.
VVT calmed that down a lot.

[Pavett1990]

I know the vauxhall VXR range are very popular with having Remus exhausts fitted (same as TTE) and with the turbo fitted pops and bangs every gear change.. Sounds amazing.. Astra VXRs sound amazing with Remus exhaust also

[E]

Having no cats at all helps quite a bit.   s:wink: :wink: s:wink:

[Anonymous]

When I had just the janspeed exhaust it did just that, so its probably down to a catless thing.

[dcod]

I don't think it's really about being cat-less (although it probably helps). I have a sport cat on my 2zz and it pops and bangs. I've heard many brand new Fiat 500 abarth's making stunning noises too. A lot of it is due to an engine that creates excessive fuel (2zz is known to run rich and turbo cars obviously can create excessive fuel on over run). I think it's also due to the make up of the exhaust and whether it can light the fuel towards the rear. Most cars probably pop and bang but it happens too far up the exhaust to hear it.

[StuC]

My Janspeed popped a little before the pre-cats were taken out. More when they were taken out and a little quieter when I had a new main cat added back in.

[andyroo104]

The Che exhaust sounds exactly as you have described.
Andy.

[jinxedkitten]

My baby is always farting (popping) away to herself. She has no precat but does have main cat. She has an after market exhaust system, but I don't know what it is, something dual pipped and quad tipped.

It tends to happen when I've been going 3k to 3.5k rpm ish, then brake (foot brake, not engine braking) and quickly drop to 2k or less, then press the loud pedal to speed up again. Going over speedbumps is a good example.

[Jrichards20]

Mine makes a nice pop every now and then. I have precats and main cat. But I do have an after market exhaust. I have Cobra quad exit. Which sounds like the same one that jinxedkitten has. Mine tends to happen when dropping from high revs to low revs. Possibly the exhaust?

[dcod]

Going over speedbumps is a good example.

Exactly what I get, just as I start to press the fast pedal over a speed bump I get a pop ... keep thinking my car is scraping over the sleeping rozer   s:o s:o

[jinxedkitten]

Jrichards, I don't suppose you could pm me a pic of your exhaust please so I could see if we have the same, then ill know what mine is! Been trying to identify it against other pics on the forum, but no luck.

I love the noise mine makes, wouldn't swap it for anything  s:) s:)

[Flipside]

My cobra makes lots of burble and pops on over run too, love it.

[eynonz]

My Longlife system also burbles on pops on the occasion when i'm dropping revs.  s:) s:)  *Brrrmm brmmm brrrm pop brrmm brmmm*   s8) s8)

[Jrichards20]

PM Sent Jinxedkittin.

If you want to show me a pic of yours I will be able to have a guess for you  s:) s:)

[AndyM]

Thanks all. Interesting information here.

I'm still a little confused as to how cat-back systems alone have such an effect as surely the 'pop' is still happening before the cat. I presume it just means you can hear the natural pops a bit better.

[Two's Company]

My H&S is popping and growling at the moment.  I think it's the heat - but not sure why?!  Tends to be more noticeable when the car is well warmed up which happens more quickly in this heat.

[jinxedkitten]

PM Sent Jinxedkittin.

If you want to show me a pic of yours I will be able to have a guess for you  s:) s:)

Thank you much appreciated, ill take a pic when I leave work.

[Jay67]

my Cobra like Flipside's pops and burbles a plenty too, sounds great  s:) s:)

[Flipside]

Mine does it more now I have swapped the manifold.

[AndrewMason]

The best (or worse) pop and bang I had was on my old Triumph (car). Did the silly thing of coasting downhill in gear with ignition off - can't remember why. Turned on the ignition at the bottom and completely blew out the sidewall of the silencer. The power of unburnt flue!

Whilst getting it sorted, due to an incorrect supplied exhaust part, I ended up driving the car with just the front down pipe - i.e. about 2 foot of 40mm plain tube only. Got pulled by the police due to flames being visable under the car on over-run. Opps...

Good news in the end as I replaced it with straight through single box system which tooted wonderfullly at 4k rpm.

[ray835]

my Cobra like Flipside's pops and burbles a plenty too, sounds great  s:) s:)

ditto same here