Backfiring, bang bang

[Rufes1]

Hey hey
well the other day i saw a nice plain sprinter in a car park hold it in first, compression brake to slow down to a speed hump, and see this flame pop out for a split second, like a flash and a big bang.

Talking to a mechanic friend of mine he mentioned a technique called key banging it... Tried this where u boot it in 2nd or third, keep ur foot down and at about 3 - 4k switch off the ignition, give the pedal a pump then flick it back on.

I got little bangs, granny farts compared to the one this sprinter did. I think the sprinter had the original engine in it.

I have an 89 civic, dual carb :).. just wondering if n e one knows other techniques to get a big bang, but none of this spark plug in the exhaust rice business...

[tofu R]

hahaha ..
um buy my car ..

[Rufes1]

Lol, how do u get urs to go bang?

[bennjamin]

IF you own a carby car ( or are just driving one...and are up for 3 secodns of fun ) sit in hte car whilst it is off - and pump the accellerator many-a-time.

Then...turn the ignition.

Should result in a HUGE ass oily big bang ! :P

BTW dont do this.

[tofu R]

hahahaha buy my exhaust ? =P and ull know

[madgrk]

Buy a supercar :? WDF would you wanna backfire your car for man?!? Oh well whatever floats ya boat I guess :)

[XXpl0Sive]

People try to prevent backfire, not try to cause it!
Why do you want to cause your car to backfire anyway?

[CTR Coupe]

dont you know a missfiring system makes it go faster :P LOL
key bangers are really bad for the car. if u want to pop flames just get a rotary :roll:
on a side note i saw an excel with one of those sparkplug jobs it had a 2F2F style 1ft blue flame for about 30 seconds

[XXpl0Sive]

Yeh that's right...that extra kick of black smoke gives you that extra push in the opposite direction right!

:)

[[[d a n n y]]]

that's gay

[UR2L8]

Rufes1: why would you want your car to backfire? just coz its in "unrealistic" Fast and Furious dosent mean its good. If a car backfires as much as you say it did, then thats VERY BAD i know that. Happens mostly on old cars, but dont try and do it, unless you can afford rebuilding your engine.

[poid]

my mate managed to blow the crap out of an exhaust on a van doing a key banger. Basically he turned it off while going down a hill quite fast, causing a rather large amount of fuel to get into the exhaust.

When it turned on there was a huge bang and bits of exhaust were everywhere

Would work better on cars without cats as well

[Rufes1]

If you cared to read my post thoroughly, u would see that i do not want it such as fast and the furious.

I am purely trying to find out different methods that cause it, and why it happens apart from fuel getting into the exhaust piping.

I also notice it happens a lot in boosted cars, but dont know why.

As far as rebuilding my engine, with my carby engine, backfiring is not necassarily that bad for it. in fact it occurs naturally when compression braking.

[joneblaze]

lol@ppl giving rufes shit before knowing what and why he was asking.
People seem to jump on the Rice/FnF bandwagon awful quick nowadays.....

[XXpl0Sive]

I also notice it happens a lot in boosted cars, but dont know why.


Generally, because they are not running their factory plumb-back BOV. They are either running no BOV or running an atmo-venting BOV. When running no BOV, instead of air going back through the system, it is forced to go back out the way it entered - through the pod filter and AFM. When running atmo-venting, sometimes not all the air is vented, so flows back.

AFM detects air going through (heading back out through the pod), so injects fuel - however, in reality, there is no extra air in the engine, hence you run a bit rich everytime this air is forced out through the AFM (when you let off throttle) and you'll get a large pop in the cat.

Long story short, their A/F ratios are temporarily screwed when letting off throttle.

[Rufes1]

this "key banging" method, could someone explain the prcess that causes this and why it is so bad for the engine? to me it just sound like when i switch it off the throttle stays open in the carb whilst the crank is still turning and thus fuel gets passed through the engine into the cat,

when flicked back on the fuel in the cat ignites giving a bang.

Dont really see how this is bad.

[ckkl]

just wondering if n e one knows other techniques to get a big bang, but none of this spark plug in the exhaust rice business...

...because that would just be ghey as wouldn't it... :x

[UR2L8]

Ok, found out something about why it happens. Ok, well it happens mainly on cars that dont have a muffler or a sports muffler and no CAT at all. Its because the ignition gets delayed or something. Oh and it happens more on straight through exhaust more.

[Rufes1]

what about the key banging thing??

[bennjamin]

this "key banging" method, could someone explain the prcess that causes this and why it is so bad for the engine? to me it just sound like when i switch it off the throttle stays open in the carb whilst the crank is still turning and thus fuel gets passed through the engine into the cat,

when flicked back on the fuel in the cat ignites giving a bang.

Dont really see how this is bad.

The thing is , this "process" dosent pull fuel or air or any mixture into the cat - "pumping" the go pedal while off does nothing but spquirt excess fuel into the chamber....nothing else is moving, not turing over etc etc.

And , so when u "turn on" ( ignite the mixture) IF it isnt flooded ( too much fuel, drowning the spark) the lot will explode in a huge bangy-bang bang !
Its bad.Just like detonation is . . .but does sound cool

[Rufes1]

no, but if u switch it off whilst in gear, and still rolling, then pump the pedal, the pistons are still moving up and down and therefore should draw the fuel u pumped in, in then out the exhaust ports in the exhaust piping...
correct?

[booget]

my understanding has always been that backfiring is caused by unburnt fuel being shunted through the exhaust... of course i'm talking out of my arse, so feel free to correct me!
(gingang, too lazy to switch boogets comp user)

[madgrk]

Just dont do it man, unless you want to ruin your engine why bother :?

[bennjamin]

no, but if u switch it off whilst in gear, and still rolling, then pump the pedal, the pistons are still moving up and down and therefore should draw the fuel u pumped in, in then out the exhaust ports in the exhaust piping...
correct?

Lets end this....guys - when the engine is OFF in any car - the pistons ARE NOT moving at all - you would know this if u ever tried to "engage" a stalled car into gear whilst rolling...hence the car jumps to a stop.While the engine isnt on / isnt producing spark the cylinders are not compressing. The only reason the engine IS moving along is that the engine is disengaged from the gearbox ( its in neutral) .

Just...dont do it. Why did this thread start ? :S

[Rufes1]

NO,
you are wrong,

if the car is rolling fast enough and you engage it in gear it goes along fine and simply compression brakes. and the pistons do go up and down

for instance if i am cruzing along in neutral at 60kmh then switch the car off, then put it in third and let the clutch out it goes along fine and the pistons are going up and down, at about 2500rpms... howver no spark is being produced and no fuel is being injected.

If you have a manual car you can do this, go at about 70k's in third and then turn it off, dont take it out of gear, and you will notice apart from loosing your gauges and if u put ur foot on the accelerator u dont go any faster nothing changes. Your engine is still clicking over at the same revs however you will be slowing down (compression braking). AND the pistons are going up and down,.

duh.


Why did this thread start ? :S

Because this is a technical forum and I wanted to know why and how it happens. So please dont troll

[bennjamin]

NO,
you are wrong,


No i am not :)
Sorry champ - I was referring to " being in neutral and off"
Ok - When the engine is disengaged and off( in neutral as i said)- the pistons are not moving at all.

You are talking of "2nd gear starts" etc ( when ur battery is dead) which forces the engine to turn over to produce spark and ignite.That is the only time that it would "suck through" apart from actually being on.
Sheesh. *stops being troll*

[Rufes1]

" being in neutral and off"


ok well you can see how


Lets end this....guys - when the engine is OFF in any car - the pistons ARE NOT moving at all

Can be misleading...

So can anyone answer my questions or is this thread going to go in circles? :shock:

[bennjamin]

I apoligise to anyone that isnt my brain :P

And so to what you said - isnt it since this guy wascompression braking, and that likely it would of been running quite rich (being a turbo) that the turbine simply blew thru alot of pure fuel , igniting after the cat and BANGING out in a flame ? From what ive seen it only ever happens on Hi-po cars , when they back off - the computer is still running at a similar A/F ratio under hi rpm or low- so when the rpms as suddenly dropped my educated guess is that it runs excessivley rich to protection ?

WE need a nerd here...

[Rufes1]

nah, i said in my original post I was pretty sure it had the stock engine in it./..

mebe no cat??

[ckkl]

Why is the sky blue? Why? :|

[madgrk]

Coz :D