Pops and bangs

Pops and bangs

Author
Discussion

JumboBeef

Original Poster:

3,772 posts

176 months

Wednesday 19th November 2014
quotequote all
Why does my 400 pop and bang on deceleration so much. I mean, I love it but what can I say to people who ask why it is "backfiring"?

V8 Fettler

7,019 posts

131 months

Wednesday 19th November 2014
quotequote all
Is it a flapper? Fuel burning in the exhaust = distant artillery fire. Adjustments can be made to the overrun valve to reduce this, but - strangely - Wedgeists are always too busy fixing more important issues.

mrzigazaga

18,534 posts

164 months

Wednesday 19th November 2014
quotequote all
The only way to get a hotwire to pop and bang is to gun it then release the loud pedal quickly...A flapper will pop and bang quite happily at most speeds..Even if you drive it conservatively...(Whatever that means)..Mind you Delilah used to pop and bang like an AK47 and she was Mechanical Fuel Injection...I still laugh at the bank holiday police horse saga...hehe

Perhaps its a TVR thing...Although i have never heard a Griff or Chimaera do it...The best was a friends Cerb that popped and banged like a gatling gun and spat fire at the same time...
I believe its to do with a slight over fuelling but then mine passed the MOT with spot on emissions...???

smash

2,062 posts

227 months

Wednesday 19th November 2014
quotequote all
Small leak in the exhaust will do that - my old V8 7 had a leaky slip joint and it sounded like a calvery volley on over run - bloody awesome!

When Caterham took on the K series engine they weren't happy about lack of pops and bangs on lift off as the ECU shut the fueling off - so they went back to Rover to get them to repgrogram the ECUs so that fueling wasn't shut off on over run.

Edited by smash on Wednesday 19th November 08:59

pjac67

2,040 posts

251 months

Wednesday 19th November 2014
quotequote all
mrzigazaga said:
i have never heard a Griff or Chimaera do it
You should get out more Mark....

here's an old (crappy) vid. of my car but you get the picture, sorry noise..

https://www.youtube.com/watch?v=8Cxt1kpxcCQ














Still doesn't sound as good as a Wedge though....

V8 Fettler

7,019 posts

131 months

Wednesday 19th November 2014
quotequote all
Flapper pops and bangs are due - in part - to the lack of road speed info being communicated with the ECU, hence fuelling continues on the overrun (ECU "thinks" car is at rest and idling, therefore needs fuel), IMO.

gmw9666

2,734 posts

199 months

Wednesday 19th November 2014
quotequote all
pjac67 said:
You should get out more Mark....

here's an old (crappy) vid. of my car but you get the picture, sorry noise..

https://www.youtube.com/watch?v=8Cxt1kpxcCQ



your griff sounded blinking great Paul at the NG event.......aural delight










Still doesn't sound as good as a Wedge though....

mrzigazaga

18,534 posts

164 months

Wednesday 19th November 2014
quotequote all
Thanks for that Paul...I feel like i have just been kidnapped by a lunatic who owns a pig farm whom i owe a substantial amount of cash to...laugh
Okay...I will re-phrase what i said...I have never heard a Chimaera pop and bang....ears..Yet....smile

adam quantrill

11,535 posts

241 months

Wednesday 19th November 2014
quotequote all
I had a chimp go past me the other way this morning. I didn't hear it - full stop!

(Hello if you're looking)

Waynester

6,324 posts

249 months

Wednesday 19th November 2014
quotequote all
I had my old 450 Chimaera exhaust sleeved, and it popped & banged quite nicely on the overrun after that. It still didn't sound quite as good as my Wedge does though. biggrin

KKson

3,395 posts

124 months

Wednesday 19th November 2014
quotequote all
My Wedge having a few pops up Prescott hill climb. I know I was slow - it was pouring down and slippy!

https://www.youtube.com/watch?v=1X81ivkmJPk

matt-man

2,665 posts

218 months

Wednesday 19th November 2014
quotequote all
KKson said:
My Wedge having a few pops up Prescott hill climb. I know I was slow - it was pouring down and slippy!

https://www.youtube.com/watch?v=1X81ivkmJPk
Sounds lovely... And roof down!!good work sir smile

Waynester

6,324 posts

249 months

Thursday 20th November 2014
quotequote all
matt-man said:
KKson said:
My Wedge having a few pops up Prescott hill climb. I know I was slow - it was pouring down and slippy!

https://www.youtube.com/watch?v=1X81ivkmJPk
Sounds lovely... And roof down!!good work sir smile
Some of the Griff & Chim boys seem to struggle with roof down driving, even when the suns shining.

Here's how it's done - Roof down..in the rain..proper job!

Sounds good too.. thumbup

JumboBeef

Original Poster:

3,772 posts

176 months

Thursday 20th November 2014
quotequote all
V8 Fettler said:
Flapper pops and bangs are due - in part - to the lack of road speed info being communicated with the ECU, hence fuelling continues on the overrun (ECU "thinks" car is at rest and idling, therefore needs fuel), IMO.
Thanks.

So while it sounds good, it's isn't really a good thing......?

ed_crouch

1,169 posts

241 months

Thursday 20th November 2014
quotequote all
So far as I am aware popping and crackling on overrun is caused by a lean mixture, not a rich one. The crackling is the continuation of combustion after the exhaust valve opens. The flame front travels more slowly across a weaker mixture than a stoichiometric one so the combustion does not complete until the whole shooting match is in the header primary tube. Not *terribly* good for the exhaust valve and seat in theory, but in practice I doubt very, very much it has caused any noticeable damage.

A rich mixture. i.e. raw fuel in the exhaust header will cause a f***ing great bang periodically as the mixture reaches both a flammable stoichiometry and autoignition temperature.

When the fuel pump on my old 390se died, I noticed it as I put the foot down and it crackled like a goodun due to a falling rail pressure as the injectors injected what was left of the rail pressure into the manifold, luckily not 50 yards from my house.

I understand the 14CUX system has an overrun cutoff? That would explain why the hotwire systems don't tend to crackle. The flappers were wild for it. When I Megasquirted mine I have to say I did play with the overrun bins on the map to retain the crackle!

Ed.

DEKE

224 posts

199 months

Thursday 20th November 2014
quotequote all
Hi All
Still look in a lot .. my 350 popped and banged, was great and I miss it something terrible nothing else will ever come close to that in my opinion, I had never heard it from behind until the day I sold it and the guy drove off down the single track road from my house and gunned it.. I said to the wife .. what the f..k have I done
Cheers all Deke

JumboBeef

Original Poster:

3,772 posts

176 months

Thursday 20th November 2014
quotequote all
ed_crouch said:
A rich mixture. i.e. raw fuel in the exhaust header will cause a f***ing great bang periodically as the mixture reaches both a flammable stoichiometry and autoignition temperature.
A classic "backfire"?

mrzigazaga

18,534 posts

164 months

Thursday 20th November 2014
quotequote all
ed_crouch said:
When the fuel pump on my old 390se died, I noticed it as I put the foot down and it crackled like a goodun due to a falling rail pressure as the injectors injected what was left of the rail pressure into the manifold, luckily not 50 yards from my house.
Hi mate...Thats what happened when mine failed on the 350i..But unluckily i was 6 miles from home...frown

matt-man

2,665 posts

218 months

Thursday 20th November 2014
quotequote all
I might get one or two pops from mine....
TVR 400se exhaust rev: http://youtu.be/TzGeEP92mG4

smile

smash

2,062 posts

227 months

Thursday 20th November 2014
quotequote all
ed_crouch said:
So far as I am aware popping and crackling on overrun is caused by a lean mixture, not a rich one. The crackling is the continuation of combustion after the exhaust valve opens. The flame front travels more slowly across a weaker mixture than a stoichiometric one so the combustion does not complete until the whole shooting match is in the header primary tube. Not *terribly* good for the exhaust valve and seat in theory, but in practice I doubt very, very much it has caused any noticeable damage.

A rich mixture. i.e. raw fuel in the exhaust header will cause a f***ing great bang periodically as the mixture reaches both a flammable stoichiometry and autoignition temperature.

When the fuel pump on my old 390se died, I noticed it as I put the foot down and it crackled like a goodun due to a falling rail pressure as the injectors injected what was left of the rail pressure into the manifold, luckily not 50 yards from my house.

I understand the 14CUX system has an overrun cutoff? That would explain why the hotwire systems don't tend to crackle. The flappers were wild for it. When I Megasquirted mine I have to say I did play with the overrun bins on the map to retain the crackle!

Ed.
I may have missed something but who said it was down to rich mixture?