Backfiring question

[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...

Also is this key naging technique very bad for the engine? if so could you please explain?

thanks again

[MagicRat]

Well, dumping unburned fuel into the catalytic converter is not too good for it, assuming you still have one. Also the vapour has a tendency to accumulate in the muffler, then ignite and will swell it up like a trash can, which is the only thing the muffler would be good for, after a while.

[MagicRat]

one more thing, a properly working converter, if you have one, should burn all the excess fuel vapour in the exhaust, making a backfire unlikely.

[ellinas]

This think is happening in the most racing cars...
In order to do that you should not have a catalytic converter adn you should have a "straight" pipe...
In the most of the time this thing is happening while you are changing gears because unburned gas iscomming out...and YEAH IT'S AWESOME

[SaabJohan]

Doing this will effectivly destroy the catalytic converter if you have one. I friend of mine broke his silencer while doing this.

This will not work on fuel injected engines and it's not the reason why racing cars bang or throw flames.

Racing cars bang/thow flames because:
- they shut off ignition for gearchanges but not the fuel
- fuel is added to cool the combustion chamber when engine braking
- ALS or launch control is used to keep the turbo up to speed

[leadstriker]

This big bang theory is quite common in rally cars where they try to up the rpm by injecting fuel and igniting it in the exhaust. They do this to keep the turbo running effectively.
An addditional injector and spark plug or cylinder shut off would give you your kick . But do emove the cats before yo do this.