Corsa Sport Gav
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Registered: 12th Feb 03
Location: Durham, County Durham Drives: A6 Allroad
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always back fire? 
[Edited on 02-10-2003 by Punto_Gav]
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vibrio
Banned
Registered: 28th Feb 01
Location: POAH
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they do not
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kerzo
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Registered: 10th Nov 02
Location: Norn Iron
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why do they back fire sometimes then?
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Corsa Sport Gav
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Registered: 12th Feb 03
Location: Durham, County Durham Drives: A6 Allroad
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9 times outa 10 they do
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Corsa Sport Gav
Member
Registered: 12th Feb 03
Location: Durham, County Durham Drives: A6 Allroad
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either they back fire or its a shity blow off valve
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vibrio
Banned
Registered: 28th Feb 01
Location: POAH
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no it is just the rumble of the exhaust
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kerzo
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Registered: 10th Nov 02
Location: Norn Iron
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why are rally cars so noisy?? surely they should get some silencers on and drive more carefully...all the commotion could startle a stray sheep
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X3DOS
Registered: 1st Jan 70
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When you change up on a properly mapped turbo car fuel ignites in the exhaust upon liftoff, its called liftoff correction - overrun. It ignites making flames and pops. Its normal. Acts to cool cylinder chambers.
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X3DOS
Registered: 1st Jan 70
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ps my punto used to do it all the time. Sound like explosions.
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Corsa Sport Gav
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Registered: 12th Feb 03
Location: Durham, County Durham Drives: A6 Allroad
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o right, cheers m8y
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starkmotorsport
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Registered: 27th Apr 02
Location: Scotland
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They backfire because there is often fuel vapour still ignited as it exits the exhaust, so when it reaches the end pipe and oxygen in the air, it explodes.
Also, rally cars are noisy because their engines are working overtime, there are rocks bigger than your fist constantly hitting off the bottom of the car and basically they're noisy because they're competition cars, and thats what they do best.
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starkmotorsport
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Registered: 27th Apr 02
Location: Scotland
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quote:
Originally posted by X3DOS
When you change up on a properly mapped turbo car fuel ignites in the exhaust upon liftoff, its called liftoff correction - overrun. It ignites making flames and pops. Its normal. Acts to cool cylinder chambers.
Kinda true but not just turbo'd cars do it. My 205 back fired like a b'tch when I was peddling it hard.
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ianofbhills
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Registered: 10th Feb 01
Location: newcastle
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lift of correction over run WTF??!!
erm isnt the popping noises anti lag
[Edited on 02-10-2003 by ianofbhills]
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Stoneyginger
Premium Member
Registered: 25th Jan 01
Location: Stonehaven, Aberdeenshire
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quote:
Originally posted by kerzo
why are rally cars so noisy?? surely they should get some silencers on and drive more carefully...all the commotion could startle a stray sheep
Its called having a quaife or similar straight cut gearbox. Whining from the gearbox is a lovely noise
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Skipz
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Registered: 23rd Aug 03
Location: Falkirk: Drives:nothing but gettin another Corsa
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my dad used to have a car that done that, way back when he started driving donkeys years ago! he later found out the old bugger was knackered when it stopped dead on the motorway about 60 miles from home, 
Life's so easy for us aint it!
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X3DOS
Registered: 1st Jan 70
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Antilag is only really used on launch.
I havent really ever seen a rally driver who ever goes into vacuum.
You can have partial antilag that doesnt destroy the manifold and turbo so much by only preventing the engine from going into vacuum. But normally rally drivers are always flooring it.
Anti-lag is a very fast popping accompanied by plumes of black smoke.
Also isn't a back fire normally associated with a misfire on throttle so power loss occurs, these are lift off bangs, so not back fire as such in the typical sense.
The other noises are the churping external wastegates used.
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3CorsaMeal
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Registered: 11th Apr 02
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don't they all just buy flamers kits to look cool, because neons will get broken too easily?
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Gambit
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Registered: 5th Jun 00
Location: Common Sense HQ
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quote:
Originally posted by X3DOS
Antilag is only really used on launch.
how do you work that one out?
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3CorsaMeal
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Registered: 11th Apr 02
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on the rally driving day i did, one of the blokes who was there for the day, commented on how the evo, sounded like "a skeleton having a wank in a metal dustbin"
and we had a convo about dump valves, and the rally driver said "yeah, it got a proper one, not one of these barry boy things that goes "ptssssch" like opening a can of coke"
i was stiff
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Jason Iles
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Registered: 19th Jun 01
Location: Bristol
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quote:
Originally posted by 3CorsaMeal
on the rally driving day i did, one of the blokes who was there for the day, commented on how the evo, sounded like "a skeleton having a wank in a metal dustbin"
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Tom
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Registered: 3rd Apr 02
Location: Wirral, Merseyside
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@ 3cm u always manage to lighten up my day
Quality.
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neoquip
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Registered: 12th Aug 02
Location: Nottm
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straigh through zorst pips.. small silencers.. hi octane fuel.. and atmosDV all help to get the POP... like said above
this is beacuse fuel is still in the zorst and it flames/pops when it burn with the oxygen
I like my car poppin on gear changes!
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X3DOS
Registered: 1st Jan 70
User status: Offline
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quote:
Originally posted by Gambit
quote:
Originally posted by X3DOS
Antilag is only really used on launch.
how do you work that one out?
[refraining from taking the piss]
When you launch at the beginning of the rally you want to accelerate as fast as possible, so you pull away from 0mph straight into boost instead of being bogged down by lag.
[/refraining from taking the piss]
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Gambit
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Registered: 5th Jun 00
Location: Common Sense HQ
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XEDOS - u are thick as pig shit, i was tryin to refrain from this, but that last statment jsut lit the touch paper for me.....
so here goes
Basically, on a poorly mapped road car or aggressively mapped motor sport car the mapper will often only really spend time mapping at full throttle load points and neglect the part throttle map often running the car rich at these load points on the map (running to much injector duty at these load points). This is what causes the black smoke/yellow flame on lift off/gear changes..
Cooling of the cylinder chambers as u call it can't happen by igniting fuel/fuel vapour in the exhaust or the exhaust manifold when it is hot!! this just makes things hotter as it is an uncontrolled burn of fuel.
Lift off correction, this term is total cr@p in your context. U can have fuel correction tables that are referred to by the map but these are used in conjunction with temp correction maps. Both of these tables are referred to when running MAP sensors and air temp sensors (usually ECU's such as Motec, Gems, Autronics for motor sport) or as with the majority of turbo cars a MAF (mass air flow) sensor which creates a Karrman Vortex within the MAF (use of cylinders to interrupt airflow and create a vortex behind the cylinder). The Frequency is then measured to determine air mass and flow figures. This frequency is measured In Khz (Karrmen hertz). Fuel cut on a standard EVO 6 is 1500Khz i.e the point where to much air is being introduced and the engine could run lean.
Overrun - Overrun is what happens on cars when the combustion chambers have carbon deposits on them due to running too rich and not achieving a correct burn. The the red hot carbon deposits then ignite any remaining fuel vapour in cylinders after turning off the engine cause it to overrun.. Overrun may also be used as term for retarding the ignition on throttle lift off, but this is being used in the wrong context as it relates to antilag.
What you are trying to say is :
You run slightly rich at certain load points on the map, usually where the Torque and bhp plots would cross on a dyno print out and also at the top end. This is where the engine is under max load and is the hardest point to map. Running a little rich helps to keep down detonation of the fuel/air mix due to the increased cylinder pressures at this point. (Cylinder pressures increase in the midrange (usual point of max load) as ignition settings are advanced in the map to create power, boost is increasing rapidly as the turbo is spooling up hard and spiking as the actuator attempts to control boost). Running a little rich also help retard the flame front within the combustion chamber causing a slower burn (hence less hot) which cools the top of the piston crown area.. Running a little rich at the top end where max ignition advance is being run is also done for the same reason to stop det. When u run a little rich you don't get a full burn, hence partially burnt fuel is mixed with exhaust gasses and ignites in the manifold and sometimes the exhaust causing the flames. the only reason u see the flames is cause the CAT has been removed other wise u wouldn't see it.
Running too rich and actually igniting raw fuel the exhaust manifold is a really bad thing creates mega heat and kills turbos + manifolds.. You need to closely monitor EGT's (exhaust gas temps) on turbo cars when mapping, EGT's should not be past 900 - 950 deg C. running very rich will also cause problems with bore wash (fuel getting past the piston rings and getting into the oil in the sump).
Igniting raw fuel in the manifold is only usually done when running aggressive anti lag (aka rally cars where they change turbos after every event). Anti lag is method of keeping the turbo spooled up between gear changes and when off the throttle. This is achieved in a no of wayz, but the most common is using a throttle kicker (jacking the throttle open), retarding the ignition so the extra fuel remain unburnt and then igniting it in the manifold keeping the turbo spinning. This causes the loud cracks/bangs and flames u see with rally cars.
Running aggressive antilag all the time on a road car would cause the turbo to expire in less then a couple of thousand miles..
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Jason
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Registered: 5th Aug 03
Location: Northern Ireland
User status: Offline
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thats a waste of typing... doubt any1 will read it
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