# Flames/backfire on over-run/gear change



## leeroy_25 (Dec 19, 2006)

Odd question! just curious.. I just wondered what causes the flames and popping when you lift off for gear changes or on the over-run? I thought it was un-burnt fuel and cold air i the exhaust?
My old car used to do it a lot but my new car doesn't seem to do it so much? Is it something in the tune.. Is it better that is does do it or does not?!

Cheers
Lee


----------



## jim-lm (Mar 15, 2005)

Mine done it all the time, it had a rich tune and de-catted.


----------



## DrGtr (Jul 18, 2009)

It started doing it since i have removed the cat, seems to be over reach which is not good for the engine i hope i will not brake it due to been overreach.


----------



## D-Ranged (Aug 16, 2007)

I always thought it was unburnt fuel igniting in the exhaust when its hot


----------



## Mookistar (Feb 5, 2004)

Removing the cat will make it audible


----------



## Marky_GTSt (Dec 31, 2005)

It is just fuel being burnt in the wrong place ie the exhaust, In answer to your question, Yes its probably better if its minimized especially if you have a Cat converter as the extra fuel can overheat the cat.(not to mention wasting fuel) As Mook in a roundabout way said, the noise is always there to some degree and a louder exhaust and decat will show it up quite a lot even on an otherwise stock car.

Older cars (especially with carbs) used to do it as they went out of tune or just from general wear. or from revving the car hard in 3rd, switching off the ignition and pumping the throttle (even better if there was an accelerator pump fitted) , on switching the ignition back on you could get a shotgun effect that quite quickly ruined your silencer but could be fun to scare the unwary pedestrian 

Anti Lag systems do it to an extreme on purpose to keep the turbo spooled, But its hard on the manifolds and turbos so they need more regular servicing.

What was your old car, and what is your new car ? are we talking RB`s here or something else ?


----------



## leeroy_25 (Dec 19, 2006)

My old car was a gtr too. Stock twins. Decat pipe and tune. New car is rb30 big single and 3.5" system through to the back. Is actually very quiet compared to the old car strangley? Maybe due to turbo size? That said it sounds like the world is ending when the screamed pipe opens! ;-) The current tune is a bit rich too so I am surprised I don't get the backfires?!


----------



## Miguel - Newera (Sep 18, 2003)

Most ECU's can easily be set to switch off fuel on over-run, incl. Power FC's. 
This will reduce backfiring on gear shifts, etc.


----------



## ehnus (Feb 22, 2010)

i love that my R32 does this


----------



## NISFAN (Oct 11, 2003)

Vent to atmosphere BOV fitted?


----------



## leeroy_25 (Dec 19, 2006)

No BOV on my current car.. Had one on my old car though?? Why would that make a difference? So that could be the reason for me then?

Lee


----------



## Multics (Apr 27, 2008)

Edit: Re-read your post, you mention no BOV.
It would be expected to pop and bang if you vented to atmosphere though (if you have MAFs).


----------



## leeroy_25 (Dec 19, 2006)

Arhh yes... Well that seems perfectly reasonable and logical! Probably could have figured it out if I had thought about it! I guess that is also why my tuner recommended if I fit a BOV I should fit a recirc type? Not that I am planning to fit a BOV anyway..

Cheers
Lee


----------



## Nigel-Power (Dec 16, 2009)

Backfires and exhaust pops are a signature of the firebreathing monsters  

as explained above, it's the unburnt fuel particals emitted and at some point due to high exhaust temperature the unburnt fuel particals ignite into a ball of flame. At least the fuel is wasted in a spectacular fashion and doesn't go un-noticed.

Mine does it very often with gear changes and the rear bumper has somewhat lost color and texture as a result. You can put an exhaust shield to avoid stains of fuel/smoke residue left on the rear bumper.


----------



## godzirra (Sep 16, 2009)

Lee, my rb26/30 does this A LOT.

Tuning is slightly rich as it's still 'running in' tune ... although I ran it hard from the get go ie. RIPS style.

Decatted and 2 BOVs.


----------



## DrGtr (Jul 18, 2009)

Nigel-Power said:


> Backfires and exhaust pops are a signature of the firebreathing monsters
> 
> as explained above, it's the unburnt fuel particals emitted and at some point due to high exhaust temperature the unburnt fuel particals ignite into a ball of flame. At least the fuel is wasted in a spectacular fashion and doesn't go un-noticed.
> 
> Mine does it very often with gear changes and the rear bumper has somewhat lost color and texture as a result. You can put an exhaust shield to avoid stains of fuel/smoke residue left on the rear bumper.


my bumper since i have removed the cat became almost black, i hate it , i just hope it can be cleaned with a polish.


----------



## ChristianR (May 31, 2005)




----------



## leeroy_25 (Dec 19, 2006)

Bit of mild cutting compound will fix your paint! Just don't let it build up to much! Lighting up the faces of the driver/passengers in the car behind at night does put a smile on your face I have to say! I must confess I miss it a bit!!

Lee


----------



## ma19sa (Jan 27, 2015)

can this be done in the tuning ? I have catted downpipe though !


----------



## bkvj (Feb 13, 2006)

Miguel - Newera said:


> Most ECU's can easily be set to switch off fuel on over-run, incl. Power FC's.
> This will reduce backfiring on gear shifts, etc.


I'd rather have it the other way round, more fuel injected upon over-run (yes I am a tit:chuckle.


----------



## ShopGTR (Oct 4, 2007)

I've had people pull up to me to tell me my car is on fire.

Cory


----------

