backfire

zerocool85 SG

i read on the net about backfires..

too lean fuel with too much air

and too rich with too little air

is this the cause? and if it is claimed to be dangerous and unhealthy for engines/exhaust to have backfires.. why do the so called well-tuned-cars still have backfires? cars like ferrari that is stock also have backfire..

can anybody explain? to add on, i also know the difference between afterfire and backfire..

afterfire is just the continuous popping of exhaust sounds after reving.. backfires will have flames coming out..

asking this question because i saw a red f430 speeding in KG JAVA tunnel earlier on with flames coming out of his exhaust shifting up his gear and releasing throttle.

NoobBOY SG

There's many causes that cause the engine to backfire, all i can remember now is left over unburnt fuel and wrong camshaft timing

n0x SG

there are 2 reasons which i know of which cause backfire from the exhaust...

1) they install a kit at the exhaust there to make it backfire... of cos its illegal in sg...

2) the car's egine has anti-lag system or in intial d talk.. "the mis-firing system"

why does such a system exist?? bcos there is a need to counter turbo lag in turbocharged engines...

usually in a normal engine... the spark plug is tuned to detonate the fuel air mixture at top dead end.. meaning when the mixture is fully compressed... after which the exhaust is expelled...

however. in an anti lag system.. the engine is tuned such that the detonation of the spark plug in one of the cylinder is delayed... so when the rest of the cylinders detonate ... tt one particular cylinder did not.. and when the exhaust is expelled in the other cylinders.. tt special cylinder is expelling unburnt fuel air mixuter... and this is when the spark plug detonate...

so in other words... the combustion of the air fuel mixture happens in the exhuast manifold... and this drives the turbocharger.. and produce the back fire and the popping sound u hear..much like someone firing an M16....

of cos this means u have to change exhuast manifold and turbocharger frequently bcos they are literally eaten up by the flames.... 5000km if i am not wrong..

tomsss SG

... plus the catylic converter, if they didn't remove it.... and they are really expensive to replace.

zerocool85 SG

thanks for the explanation!.. however.. it doesnt make sense to me though.. if all the cylinders do not combust the fuel.. it can mean that less power is being output?

i always had the impression that performance wants all the fuel to be burnt for maximum power and also efficiency..

AE86tofu SG

not only cos of that...but also in naturally aspirated engines...its due to the valve overlap...especially for those running camshafts with long duration....meaning that the exhaust valves take longer than usual to close to help with the "scavenging" effect...but as its damn long some of the gases from the intake stoke escapes out into the exhaust valves...and the exhaust pipes and valves being very hot...ignite the air/fuel mixture....