Popping exhaust question

[rustytools]

Hi everyone.

I'll be soon replacing an exhaust on a BMW mini cooper (not S) as the rear box has a hole in it.

I noticed that when the engine is in overrun it makes a popping noise. I appreciate what causes this noise and why it does it. I read online that cooper S' are notorious for it but no mention of plain coopers/ones.

However it go me thinking. Do the majority of road cars make this popping noise when in overrun and is it just a case that exhaust systems are so quiet these days that you don't hear/notice them on typical road cars. The reason I ask is that when the exhaust was in good nick we've never noticed it making the popping noise. I'm wondering if its always made this noise and the hole just makes it noticeable.

I read somewhere online that the hole maybe sucking air when the exhaust pulse flies past and this air helps promote the popping (i'm guessing providing some more oxygen?) I didn't really understand this theory though. Could someone please explain it.

Anyway I guess I have too much time kill at work thinking about these things!

Cheers

RS

[RobCrezz]

In evos at least, you can make it pop and bang on the overrun by making the ecu retard the timing and inject fuel and also air via the sas (secondary air system). Sas isn't needed but does increase the effect.

[Special K]

Mine occasionally pops back ....

http://www.youtube.com/watch?v=W0rXnBp3GYI&con...

[Garlick]

I can't explain it, but my TVR can do 'pops' loud enough to make pedestrians jump out of their skin

[RobCrezz]

Garlick said:

I can't explain it, but my TVR can do 'pops' loud enough to make pedestrians jump out of their skin

Same here with my car. I never make it pop when I go past a bus stop, ever.

[tyranical]

You use the word notorious when describing the Cooper S exhaust pops like its a bad thing?

Its awesome, I make mine pop on purpose all the time lol.

[Special K]

RobCrezz said:

Garlick said:

I can't explain it, but my TVR can do 'pops' loud enough to make pedestrians jump out of their skin

Same here with my car. I never make it pop when I go past a bus stop, ever.

When I lift off I never touch the throttle slightly to make this happen too

[rustytools]

the popping is great! I used to live very near a S Works and that sounded superb.

I'm interested in the idea that the hole letting air in might increase the snap crackle pop. Just trying to get my head round it. I'm trying to find the link to post on here to show you guys.

That Elise being fully wrung out sounds fantastic! That overrun flash would make batman proud

[Garlick]

Special K said:

RobCrezz said:

Garlick said:

I can't explain it, but my TVR can do 'pops' loud enough to make pedestrians jump out of their skin

Same here with my car. I never make it pop when I go past a bus stop, ever.

When I lift off I never touch the throttle slightly to make this happen too

Oh yes. Bored bus queue? Low gear, big revs then lift off and tickle the throttle as you pass. That wakes them up

[Dalto123]

The 944 sounded lovely when it popped and banged Usually happened when slowing down in 2nd gear, got a bit loud sometimes....Not that im complaining

[MJK 24]

Bit of unburnt fuel on the overun usually?

My Alfasud used to do it all the time. The Elise will do it if you change up at a high rpm. High being over 5,500ish.

[Gruber]

One of my finest motoring moments was the day I caused a minor security alert outside the Old Bailey by swinging round the corner from Holborn in my old Porsche 924 just as the over-sized after-market exhaust let out a couple of very loud bangs. The sight of the assembled press corps ducking for cover is a memory that will stay with me for ever.

[anonymous-user]

On the Kent run last year I was following a Blue GTR massive pops and bangs had my passenger and I grinning like 3 year olds

[SambaS]

My Samba did it when the backbox went wrong. I enjoyed it while it lasted :bagoverhead smiley: the xr3 on the otherhand when driven hard will pop a nice blue flame out the exhaust after letting off the go pedal

[Special K]

Garlick said:

Special K said:

RobCrezz said:

Garlick said:

I can't explain it, but my TVR can do 'pops' loud enough to make pedestrians jump out of their skin

Same here with my car. I never make it pop when I go past a bus stop, ever.

When I lift off I never touch the throttle slightly to make this happen too

Oh yes. Bored bus queue? Low gear, big revs then lift off and tickle the throttle as you pass. That wakes them up

As much as I hate to admit it I do this everytime .....

[KelWedge]

When I last had the Emerald Remapped, I got asked by the nice man at Emerald, do you want it to pop & Bang?

Cant remember what I said

[Paulbav]

The Porka does it a lot on over run and sometimes when shifting on the red line, resulting in something like a shot gun going off with 12" flames to match.... I would never dream of doing this should there be any pedestrians around though

[so called]

Mines mad at the moment with the new ECU.

[KP]

My M3 pops when cold.

KP

[Fastdruid]

My bike does it spectacularly. All due to carbs and a leaking port gasket (which is an engine out job to fix). Bit of fuel into the hot pipes mixed with some air from the leak and it gives some really spectacular noises (and I'm told flames too).

Of course I'd never ever leave it in too low a gear with lots of revs to make it pop and bang on purpose, oh no.