333pg333

What are the feelings re Anti-lag? Seems to be something common to Rallying but not so common for circuit work. Can't see why not really but I understand that it shortens the lifespan of the turbo.
Discuss.

Larry Herman

Ok, I'll bite...what is anti-lag?

DanR

As i understand it:

Anti-Lag System is an engine management technique that allows to minimize the turbo lag time. (in effect keeps the turbo constantly spooled)

It works....... (quote)
When the driver lifts his foot from the gas pedal the ignition timing is altered with sometimes 40° or more of delay (retard) and the intake air and fuel supply mixture is made richer. The inlet butterfly is kept slightly open or an air injector, bypassing the inlet butterfly, is used to maintain air supply to the engine. This results in air/fuel mixture that keeps getting in the combustion chambers when the driver no longer accelerates. The ignition being severely delayed, the air/fuel mixture reaches the exhaust tubes mostly unburned. When the spark plug fires, the exhaust valve is starting to open due to the ignition delay mentioned above. Additionally, the exhaust temperature being extremely high, the unburned fuel explodes at the contact of the exhaust tubes. Luckily the turbo sits right there and the explosion keeps it turning (otherwise it would slow down since its intake, the exhaust gases, is cut-off). The effect is vastly lower response times with some downsides:

A quick rise of the turbocharger's temperature whenever the system is activated. A huge stress on the exhaust manifold and pipes (mounted on a street car ALS would destroy the exhaust system within 50-100 km)

Note that some regional or national European events prohibit the use of ALS systems while more and more WRC events regulate the noise levels allowed by competition cars effectively disabling ALS.


It sounds amazing when in action!

Larry Herman

Ok. Sounds interesting, but doesn't a bypass valve accomplish a similar thing? I always thought that it was the buildup of intake pressure when the throttle was closed that rapidly slowed the turbo. An electronically controlled bypass valve would be much more effective than the old pressure relief ones. Does this system incorporate both?

DanR

I what you are explaining is similar to new anti-lag techniques, called Exhaust Gas Recirculation (EGR) which is starting to become more popular

d15b7

hi larry.

i think that the WRC type antilag systems actually 'overfuel' or use some type of computer controlled fueling scheme to keep the turbo spinning up very fast, even as the driver is removing his foot from the accelerator....

if you watch some of the vids from WRC, you can hear a super fast 'pop pop pop pop' from the exhausts at weird times; this i believe is the antilag system activating.

i was also told that it is very hard on the turbo, and other associated exhaust pieces. not really suitable for anything other than an all-out racecar (where replacements such as the above would be considered 'consumables'.

todd
ReidSpeed

Geoffrey

Larry, a bypass or blow off valve simply relieves the pressure between the compressor and the throttle plate when the throttle plate is closed. While this does aid in reducing the amount the compressor slows down on deceleration, the turbo still does spin down substantially. Anti lag keeps the turbine spinning by igniting the fuel in the exhaust system and therefore keeping the exhaust velocity high which will keep the turbine speed up.

You really need an inconel based exhaust system and as mentioned it is very hard on the components. What you gain is a reduction in boost lag when transitioning back to the throttle. In road racing this usually isn't a problem because in a corner, when you transition back to the throttle, you probably can't use all of the turbo power anyway, and you don't want it to hit all at one time. So, the .5sec progression from no boost to full boost isn't a detriment, espeically on today's highly efficient twin turbo setups. In Rally racing, they want full boost right away to spin all 4 wheels, so here it is an applicable use of the technology. In Drag Racing it is used to build full power when staging.

MoTeC ECUs can to anti lag and it works well, however, I have not found it practical in a road racing environment.

Larry Herman

Thanks Geoffrey. Why am I not surprised that you have the concise answer once again?

333pg333

I think at this stage I'm inclined to leave the new motor as it is (or will be). The new modern turbo (Borg Warner S362 ETT) should spool very well and there will be a ton of power in this engine. On the track we generally are not below 4000rpm I'm guessing so lag shouldn't be a problem. I just am at that stage where the engine is on the dyno, so any changes should/could be made now.

A.Wayne

Correct ,

On a correctly mapped and sized system anti-lag with it's on /off nature is not practical or needed on a road course . It is highly essential for rallying due to the slow cornering speeds and mostly 90 degree turns... Works to perfection on Auto -X courses...

333pg333

Yes I can see the advantages with it in those formats. Plus it will degrade the turbine more rapildly. Unlike WRC teams, I don't have a team of mechanics waiting to rebuild anything between drives. Shame really...

Larry Herman

Is that a ball bearing turbo? I understand that they don't spool down as quickly.