TRUTH ABOUT... ANTI-LAG SYSTEMS
Anti-lag systems may be one of the most sought-after modifications available, but they are often also one of the most misunderstood. It’s time to learn the truth…
Anti-lag is without doubt one of the coolest mods you can make to a fast Ford, and if done right can be one of the most rewarding. But there are many types of ALS...
‘TRUE’ ALS SETUPS
Modern anti-lag systems offer various ways to turn a turbocharger into what is essentially a simplified jet engine, while off throttle. This can create (up to) full boost at all times, regardless of throttle position. To operate correctly, a considerable fuel/air mix needs to be ignited in the exhaust manifold and turbine housing – this provides the energy to turn the turbine wheel, and therefore the compressor wheel, at a much faster speed than it would otherwise do when off-throttle. This means the turbo responds incredibly quickly when you get back on the throttle.
ALS setups of this nature have the same requirements as anything else for combustion; fuel, air, and an ignition source. Fuel is usually taken care of by a rich mixture from the standard fuel injectors – usually supplemented by heavily retarded ignition timing so the fuel isn’t ignited within the engine (although in some instances it has been known for the fuel to be directly injected in to the exhaust manifold). The source of air is the main difference between most anti-lag setups, but it needs to be introduced to the exhaust manifold somehow, when the throttle is closed – usually there is very little oxygen reaching the exhaust, certainly not enough for a functioning anti-lag system. As for ignition, while it has been known to use a spark plug in the exhaust
system, ignition is almost always achieved by heavily retarded ignition timing allowing the spark plugs to fire with the exhaust valves open, or the incredibly high exhaust temps causing the air/fuel mix to spontaneously combust – or a combination of both.
THROTTLE BYPASS
This is by far the most common type of ALS in the Ford world. It’s what Cosworth rally cars used in Group N and Group A, and what most current Rallycross cars use. The air needed for combustion comes from the engine itself, and to get into the engine it has to somehow get past – or bypass – the closed throttle(s).
“ANTI-LAG EFFECTIVELY TURNS THE TURBO INTO A JET ENGINE WHEN OFF-THROTTLE”
The obvious problem with allowing air into the engine is that the engine would normally act like the throttle is partially open, therefore not decreasing engine speed
as fast as it should, or in some cases causing revs to rise. The solution to this problem is the same as for the fuel and ignition issues – heavily retarded ignition timing. This means the spark plug fires much later than it should do, so the engine makes much less power – but more importantly it also means that the exhaust valves will be open when the spark plugs do fire. This means that most of the fuel injected into the engine is already exiting the cylinder and is in the exhaust manifold/turbine housing before it is ignited by the late-firing spark plugs – perfect for keeping the turbo spinning. The effectiveness of throttle bypass style ALS revolves around how much air can be bypassed, and this can range from anything between zero engine vacuum, right up to virtually maximum boost levels.
However, as with all forms of ALS there are downsides. The first problem doesn’t affect Cosworths due to the electronic servo, but many cars that use a traditional servo operated by the engine’s vacuum pressure will be affected. Obviously when ALS is active, the engine no longer produces a vacuum – and often makes positive boost – so the servoassisted brake pedal goes rock hard! Another issue is temperature. While there’s no escaping high exhaust temps with any form of rally-style ALS, the throttle bypass systems tend to be among the worst, causing particularly high in-cylinder and exhaust port temperatures.
THROTTLE KICKER
This style is very similar in operation to throttle bypass ALS, but instead of bypassing a closed throttle it actually opens the throttle slightly to allow the air past, despite the driver’s foot being completely off the accelerator pedal. This is done using an electronic fly-by-wire throttle, and the ‘throttle kicker’ is an ECU-controlled secondary way of partially opening the throttle. On more basic set-ups, often seen on Group N rally cars in order to comply with the regulations, the throttle can be modified so that it never fully closes. The fuelling and ignition is adjusted accordingly, in much the same way as with throttle bypass systems. As such these systems enjoy the same benefits as throttle bypass, but also suffer from the same drawbacks. Plus, the permanently open throttle also causes high and very rough idle speed, as they require heavily retarded ignition timing to prevent the engine from free-revving while off-throttle.
EGR ANTI-LAG
While EGR stands for exhaust gas recirculation, contrary to popular myth there’s no actual exhaust gas recirculation going on. These setups do resemble EGR pipework and valves, but actually work in the opposite direction, and would be more correctly called a ‘fresh air system’. This system is what almost all modern WRC cars run, including all Ford WRCs from the Escort WRC onwards.
‘EGR’ anti-lag works by allowing air to flow from the engine’s boost pipes directly to the exhaust manifold once activated, completely bypassing the engine altogether. This is done using either a pneumatically activated EGR style valve (often fitted with a non-return valve to prevent any exhaust gases entering the inlet system), or a more sophisticated version using fully electronic valves. The fuel and ignition source is the same as the previously mentioned ALS setups, although
the ignition doesn’t usually require as much retardation, and the heat of the turbo alone can often serve as the ignition.
This form of ALS can work either alongside or in place of a throttle bypass system, and while it adds complexity, it also aids reliability due to less heat created inside the engine, and will also allow vacuum assisted brake servos to remain fully operational too.
“ALS CAN GIVE SUCH AGGRESSIVE ACCELERATION MANY RACE CARS WILL HAVE ADJUSTABLE SETTINGS TO LESSEN THE EFFECT IN THE WET OR ON GRAVEL”
ROCKET ANTI-LAG
This setup is something very special indeed, and while we’ve only seen it fully functioning on Subaru WRC cars so far, there’s no reason it can’t be implemented on any other car. The general idea is the same as with most other ALS systems – to turn the turbo into a mini jet engine when off
throttle – but the rocket system integrates a very small jet engine-style combustion chamber and flame tube in to the pre-turbo exhaust system. This makes it incredibly efficient and effective – up to 3Bar of boost is possible at barely above idle speed! Impressive stuff.
However, these can be very complex systems to package and install (the rocket itself needs to be at least six inches long) and will require very sophisticated software to control fuelling, airflow, and turbo rpm – without this, the turbo would just destroy itself in seconds. Not an ideal outcome!
ALTERNATIVE ALS
If a ‘true’ anti-lag system isn’t suitable for you, there are a number of other options that could help, which are effective, but a lot less extreme in operation as the previously mentioned anti-lag systems. Admittedly, none offer the same level of performance as ‘true’ ALS, but they are viable and almost sensible options to consider.
NITROUS
We all know about the power boosting abilities of nitrous, but
it’s also a brilliant way to get your turbo spooled up. Although some rumours suggest injecting nitrous into the turbo, this is not how nitrous anti-lag systems work. In fact, aside from some minor electrical differences, they work exactly the same as powerboosting nitrous systems.
So how does it reduce lag then? Well, it’s actually quite simple when you think about how an engine works. Turbos are spooled by exhaust gas, and the more power an engine produces at any given revs, the more exhaust gas is produced. Therefore using nitrous at lower rpms will produce more power than usual, and therefore more exhaust gas – so the faster the turbo will spool up.
Many nitrous anti-lag setups only run a 50-75bhp shot of nitrous. This may not seem a lot, but when you consider your average 2.0-litre turbo engine will be producing less than 100bhp at 3500rpm, even a 50bhp shot of nitrous will not only give you 50% more power (making the transition between on and off boost far less noticeable) but will produce 50% more exhaust gas too. This 50% increase in exhaust gas, from a turbo’s point of view, is like being spooled up by a 3.0-litre engine.
The main advantage over rally-style ALS is that a nitrous system won’t create the huge amounts of heat of other systems, plus it’s self-contained and doesn’t need an expensive ECU and specialist knowledge to set the system up.
The main disadvantage (aside from the potential for the gas to run out) is the fact nitrous can only realistically be activated at full throttle. This means it’s not ideal for accelerating through a corner or on traction-limited surfaces.
FULL-THROTTLE GEAR CHANGE
This is one of the simplest forms of ALS, and can be achieved very cheaply on many cars. It simply cuts the ignition as the driver puts his foot on the clutch and, as the name suggests, the driver keeps his foot nailed to the floor rather than letting off the throttle to change gear. With the ignition cut, the throttle wide open, and the fuel still flowing, the effect on the turbo is very similar to rally anti-lag.
The main disadvantage, aside from it being very harsh on transmissions, is it only works between gear changes and at full throttle, so in an on-off throttle or part throttle situation it has no effect and the turbo lag is just as noticeable as ever.