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Anti Lag systems explained.

When you lift off the throttle the engine power cuts and the turbo starts to spool down.

From this low spool state there is a delay while the turbo spins up again before it can provide any useful boost.

The aim of a driver is to get a fast throttle response and avoid any delay in putting down the power.

ALS or Anti lag is a solution to this problem, but not something TorqueCars recommends on a road car.

What are anti lag systems and are they suitable for road cars.

So what is ALS and how does it work. What are the advantages and disadvantages of ALS.

Anti lag was devised to keep the turbo spinning in a throttle off position. A very late ignition spark (~30° retart and overfuelling causes the flame front to exit the engine through the open exhaust port.

turbo-x-section

This fast moving charge keeps the turbo spinning quite quickly and ready to provide boost as soon as the throttle is pressed again.

In a rally car this is a great way to keep the power on after a sharp corner where you'll need boost immediately. Formerly a driver had to employ left foot braking and press the throttle to keep the engine revs up.

evo-induction-kitALS keeps the turbo spinning so you have boost on tap as soon as you need it.

This is a great way to kill your stock engine, as the turbo and exhaust temps will dramatically increase whilst the anti lag is on.

If you fit your engine with uprated components then ALS is potentially a good option if you want a very fast throttle response.

The aim of an ALS system is to maintain pressure in the inlet manifold. Pressures of 0 to 1.5 bar [without it you have a vacuum on closed throttle] can be achieved with some ALS systems.

Cons of anti lag

  • Turbo and exhaust temps are raise from 700° to over 1500° causing metal fatigue, oil degradation and premature exhaust wear.*
  • The sheer pressure caused by anti lag will test your exhaust joints and show any weak spots.
  • Lower engine and turbo life and worse reliability**.
  • You will kill any catalyst fitted (hence why ALS is not suitable for road cars.)
  • You'll need an electronic servo for your brakes as these will be ineffective on an ALS equipped car.

Benefits

  • Lots of boost on tap from relatively low RPM engine speeds.
  • Less engine braking when off throttle.
  • Some will appreciate the exhaust pop noises and flames.

*The heat generated is similar to the heat produced after a hard drive, it's just that this happens when you are off throttle when the car would usually have a chance to cool down a little.

**Many cars fitted with ALS have lasted 8-9 years of daily use without issue. So although reliability is compromised you're only expecting say half the normal life expectancy from these components. Most turbos and exhausts are uprated anyway on ALS fitted cars so can cope with the extra heat. Don't expect OEM parts to survive as long though.

Modern systems in cars create a way for the exhaust gases to reflow through the engine and keep the turbo spooling. EGR has the benefits of lower exhaust temps than in an anti lag system but it doesn't generally provide quite as much of a boost as ALS but is a very credible alternative.

ALS or Anti lag systems are being phased out due to tighter regulations in many motorsports events.

Most ALS kits for road cars give very little of a noticeable boost at idle, make a lot of noise and compromise reliability.

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3 Responses to “Anti lag systems”

  1. Hunting.Targ says:

    Very engaging explanation. I submit that it doesn’t make sense to alter the engine timing with OEM components – and if one is going to install uprated components such as fuel injectors, and fuel and exhaust manifold, why not just twincharge the engine and get similar benefit with less wear? Just a thought.

  2. Joel tarin says:

    Anti lag system. Is it smart or safe to install anti lag function on a bone stock 2012 wrx hatch for obvious reasons to shoot out flames here and there. Thoughts?

    • TorqueCars says:

      It’s a good way to kill a catalyst! Any unburnt fuel, or unclean combustion will eventually ruin a catalyst which in most countries is a legal requirement. However for off road use the catalyst can be removed. Personally I’d only use an antilag setup on a track/competition car.

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