Anti-lag, how does it work?

Runnah

Runnah

New member
After watching that GC8 video with all the popping and spitting, my curiosity have been sparked.

What is it exactly?

I've never seen any parts related to it, what are they if any?

 
L

Lawdawg

New member
I'm shooting from the hip here so flame away, but my understanding is that it is basically another injector IN THE EXHAUST just before the turbo that shoots in some gas that explodes and keeps the pin-wheel spin'in. Not good for cats, but sounds great

 
Runnah

Runnah

New member
I'm shooting from the hip here so flame away, but my understanding is that it is basically another injector IN THE EXHAUST just before the turbo that shoots in some gas that explodes and keeps the pin-wheel spin'in.
Click to expand...
 
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Rightseat

New member
anti-lag is pretty standard on turbo rally cars. the idea os to keep turbo spooled while you lift off throttle so that when you jump back on there is ZERO lag till you get full powah

works more or less like dawg said. it's controlled by a programmable ECU like Link or EcuTek, etc.

we had it on Tulip 2, Cassidy's late lamented GC8 WRX. When the anti-lag was enabled, it spitted and popped and backfired like The Subaru From Hades. The skeery thing about it was coming into slow corners whe you lifted off the gas, the anti-lag would keep the car plowing ahead at about 20-30 mph. No prob, except when you were coming into a 10-mph hairpin and the car just wouldn't slow down! Soon learned to snap off the anti-lag switch when approaching bends like that.

Anti-lag adds a very heavy heat load underhood, and under the footwells where the exhaust runs -- you have to put heat shields on rubber hoses and wires and such. Hood vets are mandatory if you don't wanna have a barbecue under there. AFAIK it didn't have any terrible effects on the cat.

Dave G

 
Evan

Evan

Active member
the biggest problem with them isn't cats, but shredding up turbos. as you can tell from the sound it isn't exactly linear power to the turbo. all those shock waves will break off turbine fins pretty quick (ie, <10K miles).

 
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Rightseat

New member
the biggest problem with them isn't cats, but shredding up turbos. as you can tell from the sound it isn't exactly linear power to the turbo. all those shock waves will break off turbine fins pretty quick (ie, <10K miles).
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Hunnnnh? We run with probably 100 other teams tha use anti-lag, and NOBODY has mentioned this as an issue. never seen it on the rally tecnical boards, either. i guess turbo failure is just an accepted evil on race cars, due to any number of reasons.

maybe it's an issue for street use. then again, anybody who's enough of a tech dweeb to run anti-lag on a street car deserves whatever shortened component life they run into. anti-lag is race stuff, period. it's one of the reasons anti-lagged turbo cars get like 4 mpg.

DG :
default_frown.gif


 
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robu

New member
"The Prodrive P2 also has anti-lag, which no one can explain..."

Actual explanation of how it works:

When you lift off the throttle, the anti-lag throttle control solenoid (in non-DBW throttle setups many people use the IAC or cruise solenoid, with DBW the ECU does it with the main throttle plate servo) holds the throttle plate open so that air continues to go through the engine and so the turbo doesn't "stall." The ECU also continues to inject fuel into the cylinders. Normally this would mean that the engine would rev out of control, but the ECU simultaneously retards the ignition timing so that the cylinder charge is ignited well after TDC. This reduces the power output so that the revs remain about constant. It also means that when the exhaust valves open, the cylinder charge is still burning. This causes a big load of heat and exhaust gas to go to the hot side of the turbo, keeping the boost up. Remember that a huge chunk of the energy that "runs" the turbo is heat energy. Instead of an air pedal, the throttle truly becomes a power pedal (kind of like a diesel...) When you step back on the throttle, the ECU puts the timing and fuelling back to where they're supposed to be, and you have positive manifold pressure from idle on up...

FWIW, the 07 Legacy GT's have everything needed for switchable anti-lag, except for the software: Full computer control of ignition timing, fuelling, and throttle-plate position, with user-switchable maps (SI-Drive). Wanna scare the crap out of a dealership tech? Once someone cracks the ECU, put in an antilag reflash and take it in for a "backfiring" problem... ;D

 
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LastDitchRacing

Member
Maybe I can clarify a bit. I want the STOM folks to be well informed! :)

Anti-lag(or bang-bang as some Euros call it), is a means to keep the turbo spinning when you're off throttle, reducing lag when you're back on it.

This means that the power is always there(hopefully) when you need it.

Anti-Lag is programmed using a standalone ECU. When off throttle with the anti-lag enabled, the car basically dumps fuel into the engine while changing the cylinder firing. Unburnt fuel ends up int he exhaust manifold, where the heat causes it to ignite, causing the turbo to spool.

Anti-lag can be programmed to be agressive or mild, depending on preference. If it's too aggressive, the car will pull even when you're off throttle. This can be a bad thing in slippery conditions.

Usually, we attempt to to get 0 psi of vaccuum/boost at idle with the anti-lag enabled.

Some of the WRC cars see wicked boost at idle.

Anti-lag isn't used when off stage. It makes the car difficult to drive slowly around town.

If the tune and the anti-lag are done correctly, and you use quality oil, turbos shouldn't burn out too often. Those that are running on the ragged edge will always see a higher failure rate than those that don't. We ran 25psi with anti-lag and had no turbo failures over an entire season.

In terms of Cats, antilag isn't too friendly to them due to the rich mixture. Our cat is all the way at the end of the exhaust. We've found they simply disintegrate after awhile.

Cheers! Joh

 
Mighty Subie

Mighty Subie

New member
awesome write up guys, thanks for all the info, I feel smarter now.

I'm going to promply forget everything I just read while trying to keep myself from getting too bored here at work though!

 
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Bman

New member
I was also under the impression that it quickly destroys turbos, that is why it is not used in street setups

 
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LastDitchRacing

Member
It's not used on street cars because you end up exposing your drivetrain to huge amounts of torque and risk breaking things. Not exactly what you want to have happen when you're heading out to grab a pint of Ben and Jerrys! ;-)

On loose surfaces, agressive antilag is ok because we obviously have less mechanical grip. On tarmac, it's anyone's guess as to what will break first.

We've not lost a turbo yet because of anti-lag. We shut off the anti-lag on tranist sections in rallies obviously. Most folks that eat turbos don't turn their cars well. That's why we use the excellent folks at F1 Dyno.

Now, flat shifting and launch control at topics for other threads. ;-)

Cheers! John

 
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LastDitchRacing

Member
Alright.... :)

Launch control is something that we use on the rally cars. The ECU lets us program in the RPM that we want to launch at. I prefer 5,000 RPM. This can either be switched with the same, or with a different switch, then the anti-lag. We find it's easiest to have a, "stage/transit," switch. When it's in the, "Stage," position, then anti-lag and launch control are enabled.

Lauch control is only used for launching, and this is often triggered by the ECU via input from the clutch interlock switch. Holding the clutch down for more than 2 seconds with a Link ECU will enable Launch control. This prevents it from engaging each time you shift on stage, which would damage driveline components and make the car extremely difficult to drive.

Flat shifting is designed to allow shifting without lifting off the throttle. Very few rally folks employ this as we need(and use) the throttle to steer the car. Flat shifting is used more in road cars that have dog boxes(non-syncro) to decrease the loss of foward momentum when shifting.

Cheers! John

 
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