Anti-Lag wtf does it do exactly

[Hodgo]

Hey All,

Took a freshly upgraded turbo/intercooler/exhaust/puter'd evo 8 for a run, it was hmmn ok, but still too much like most evos/wrx's in that they feel like its all to easy and no fun.

anyhoo, there was a wire not installed for the anti-lag( i assume not connected by the workshop for legality reasons) so we put in a switch and..sweet jesus its like a different car, i am now in luv with anti-lag.

so apart from uping the idle and dumping bucket loads of fuel out the exhaust flame styles.
does anyone know exactly what it does and also will it do much in the way of damage (apart from the obvious cat/mufflers)??

[EldarO]

its to reduce turbo lag, basically, the ECU will fill up a cylinder and ignite it on the exhaust stroke, while the exhaust valves are open, and this will lead the resulting expolsion of gasses straight through the turbo, and keep it spinning.

I dont know of any bad things about what it does, apart from blowing holes in exhaust pipes from prolonged use.

Eldar.O.

[Bored?]

I don't really know what to make of the "wire not connected" story, because I can't see how such a thing would have anything to do with anti-lag.

A more modern anti-lag system massively retards the ignition so that an engine produces lots of exhaust but not much power. It may also inject more fuel and increase the throttle opening.

This gets the turbo on boost at lower RPM, but results in hotter exhausts due to the incomplete combustion of fuel. This has a serious impact on the life of turbos and exhausts, which is why it is typically only used in race cars. Some systems use a thermocouple on the exhaust to disable anti-lag if it gets too hot.

[Hodgo]

wire not connected story is only that they had labeled the wire but not connected a switch, so that when the car gets defected they are not liable.(well thats my opinion)

exhaust emissions etc would not quite meet the required standard

[EldarO]

the switch tells the ECU to switch to antilag mode.

Eldar.O.

[takai]

The Evos have the capability to run antilag out of the box, as far as i know. So having that dangling wire is quite normal.

Basically the biggest damage is to the turbine wheel, which gets quite toasty and dies faster. Manifolds can normally handle it fine.

[Hodgo]

ok, maybey i did not make myself clear.

the switch is turn turn the anti lag on simple as that, the tuner even said just put in a switch...

can we move on from the switch pls

ahh forget it. Think i will do what i should have and read up on the specific puter

[roadsailing]

the technical term for it is misu-firing system.

all that fire coming out your exhaust can't be good, i'd say it would be fine for short peroiods of time, but it would probably cook your cat pretty fast.

[Hodgo]

http://www.autronic.com/technical_da...es/antilag.pdf

nuf said, thanks guys

[thechuckster]

some also do some clever shit with seqential timing - they'll either drop (e.g. no spark) or retard the spark of specific cylinders in round-robbin approach - rather than cutting the ignition across all cylinders.

E.g..
cut/retard #1, normal event for #3, normal event for #4, normal event for #2
normal event for #1, cut/retard #3, normal event for #4, normal event for #2
normal event for #1, normal event for #3, cut/retard #4, normal event for #2
etc...

The result is still very short life for exhaust turbines and nearby exhaust hardware.

Dont forget that these cars are not running the massive boost levels you find on road cars. The rally-spec'd AWD turbos have restrictors infront of the compressor inlet so power output is down compared to road-going creatures.

Some hardware relies on the clutch tigger, but one megasquirt variant uses changes in throttle position & map to work out when antilag is required.

[no_tofu_speed]

the technical term for it is misu-firing system.

Kyouchi: ..... "pop pop"
hehe.....

[Soarer_D00D]

Just watch out it doesnt blow your exhaust to pieces! I've heard of Anti Lag systems literally blowing an exhaust off the car.. Unless EVO's are fitted with an exhaust that is made to cope with Anti Lag.. I'm not sure.

[takai]

Uh, if you were managing to destroy 2mm steampipe manifolds then i would be seriously worried as to the welding ability of the person who made it. You are far more likely to destroy the turbine wheels.

There are about 4 ways of initiating antilag. Later Evos (7 onwards) even have a small bleed valve which allows air into the exhaust to promote catalysation. Early Evos drop cylinders as chucky was referring to, and also bump up the AFR slightly for that one cylinder.
Still others will do the same ignition timing between cylinders but increase the fuel delivery to that cylinder, and then retard all the timing at once. It really depends on how the ECU works.

The current trend is to add more fuel to the cylinder which you are going to retard the ignition sequence on, and then add more air inside the exhaust manifold. This reduces the chance of pre-ignition on the blazing hot cylinder, and also offers some cooling in the cylinder in question.

[sideshow]

i had antilag on my datsun 1600 with an fj20t using autroninc ecu

its awsome stuff but bit silly for the road

the backfire is very loud sometimes liek a gunshot

the turbo life is shortened so is enigne life

as my timing was 20 degrees to 30 degrees afyter top dead rather than a normal 15 or 20 before top dead

it doesnt do much after 4000 rpm or so

how u would set it up is

crack throttle to 10% or around that so that u have near 0 vacuum

this then idles engione at about 3000 to 4000 rpm

then by retarding timing and addin more fuel the revs drop to about 1500 and the turbo spools up big time its this retarding of timing the puts so much load on everything

the anti lag would run for 20 seconds each time u hit 5000 rpm
so every time u hit 5000 it restarts count for 20 seconds

if the 20 seconds went past and u didnt hit 5000 it would go into cooldown mode

with antilag off and throttle at 10% the revs would rise again
so to counter this the ecu turned of a cylinder evry revolution

but it turned of a different cylinder each time so as to not foul up a plug on a certain cylinder this cylinder drop is like a miss and once the tps opens about 4% more than the previous 10% it goes away and is like a normal engine so its like driving with a small miss just of the mark

when driving the response of the mark and between gear changes is like driving an auto while stalling it up or like flat changing without the smashing of gears

its very interesting stuff but can take awhile to set up properly

this setup i had was back in 1995 and autronic still use the same setup but maybe its abit refined these days

if u have no budget then use it

if u want yr turbo and engine to last then dont use it

[AndyTTR]

Maybe i missed it, but i dont think anybody has mentioned what anti lag systems actually do. The point of anti-lag is the keep the turbo spinning while the engine is at idle / closed throttle and therefore reduce the turbo lag effect. This is most important for keeping the engine on boost between gear changes. Jack Monkhouse explained it to us at the RoM this year - his WRX was making 1 bar of boost at idle! As mentioned, it rapes the turbine wheel but in a competition car that doesn't cover as many k's as a road car and gets regularly refurbed its not that bigger deal.

I have small vids of ARC cars with crazy anti-lag idle / backfiring that I could post if people are interested.