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Old 06 Nov 2008, 11:18 AM   #1 (permalink)
Young Scooby
 
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Anti-Lag

Good Morning All.
A question for the "Veterans" ...................
Recently I read a lot of interesting documents, regarding the anti-lag system, that keeping the turbo always spinning even when you are not pressing the gas. I saw also in some subaru garage, a wrx equipped with this feature, she has a switch on/off, his owner, when he wants he switch the button and the suby, goes (or feels) like a projectile.....
It is convenient? On the long period will damage the engine?
What is your opinion about?
cheers
max
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Old 06 Nov 2008, 12:24 PM   #2 (permalink)
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Re: Anti-Lag

My understanding of Anti-lag is that the benefits are obviously no turbo lag but as a result you will obviously wear out your turbo quicker. Don't know if it will necassarily damage your engine but i would imagine if the turbo is constantly spooling then it would effectively be on boost which will cause more stress on the engine.
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Old 06 Nov 2008, 12:26 PM   #3 (permalink)
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Re: Anti-Lag

Just found this courtesy of UK dave from a 2 and a half year old thread. Pretty much covers and sums up what I'm saying far more eloquently.

Enjoy!

How ALS works
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 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 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 (which jumps from ~800C to the 1100C+ region) whenever the system is activated
  • A huge stress on the exhaust manifold and pipes (mounted on a street car a bang-bang system would destroy the exhaust system within 50-100 km)
  • The turbo produces significant boost even at engine idle speeds
  • The explosions which occur in the exhaust tubes generate important flames which can, sometimes, be seen at the end of the exhaust tube
  • Reduced engine brake
The ALS effect is mostly dependent on the air allowed into the engine, the more air supplied the more the ALS effect will be noticeable. Consequently ALS systems can be more or less aggressive. A mild ALS will maintain a 0 to 0.3 bar pressure in the inlet manifold when activated whereas, when inactive, the pressure in the inlet manifold with the throttle closed would be in the region of -1 bar (absolute vacuum). Racing ALS versions can maintain a pressure of up to 1.5 bar in the inlet manifold with the throttle closed.
While the systems mounted in Toyota and Mitsubishi racing cars are relatively smooth and noiseless those fitted in Ford and Subaru cars are much more noisy and aggressive.
The bang-bang system owns its name to the loud explosion noises one hears whenever the driver lifts off. Most racing implementations have user selectable anti-lag settings depending on the terrain, usually three settings can be selected by the driver going from mild to very aggressive. __________________
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Old 06 Nov 2008, 08:24 PM   #4 (permalink)
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Re: Anti-Lag

Thaaaaaaank You!!!!!!!
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