Geek speak The complicated explained

Anti Lag Systems

by JEZ SPINKS

Say hello to the newest turbo tech to hit showrooms FORD’S third-generation GT may be the Blue Oval’s most advanced car yet, but it features an old-school anti-lag system borrowed from the race car version and linking back to Formula 1 and WRC’s flame-spitting turbocharged glory days.

The GT features five drive modes, and rotating its F1-style knob to either the Sport or Track modes enables the anti-lag system (ALS).

We don't know much more than Ford's F-150 Raptor also uses an anti-lag system and details remain a mystery for now ahead of the car’s international launch, but we know the trick lies in managing the throttle opening and fuel delivery.

In a nutshell, the idea is that the ECU detects when the driver has lifted off the accelerator pedal and feeds more petrol into the cylinders when the throttle is closed – igniting excess fuel in the exhaust manifold and using the resulting F kinetic energy to keep the turbine spinning quickly.

The result is instantaneous throttle response once the driver gets back on the accelerator.

As most manufacturers continue their exodus from natural aspiration in favour of turbocharging to recoup performance from more efficient, downsized engines, Ford’s move is a fascinating one in an era of clever solutions.

Twin-scroll, variable geometry, sequential and even electric turbos have all helped to reduce turbo lag in modern cars, though while most have made lumpy power delivery history there can still be a fraction of a delay even with the most successful executions.

Swedish brand Volvo introduced an alternative approach recently with its simple yet cunning PowerPulse system. Integrated into the S90's D5 sequential twinturbo diesel engine, it combined an electrically driven compressor and compact air tank.

Fresh air taken from the air filter is compressed in the tank and, when the driver gives the accelerator pedal a good prod, the compressed air is unleashed into the exhaust manifold with enough force to spin the smaller turbine from 20,000 to 150,000rpm in just a third of a second.

We’ll take the GT’s approach, however, as it promises to deliver the classic “bang-bang” rally car sounds off throttle, if not the fiery tailpipes.

Igniting excess fuel in the exhaust manifold keeps the turbine spinning

Fuel tactics

ALS's genesis in motorsport ALS's genesis in BIG WINGS, big power.

The 1980s were the truly wild era of Formula 1 and the World Rally Championship, and turbo power was the common denominator.

By the middle of the decade, F1 cars were smashing 1000kW-plus with qualifying-spec engines built to last just a handful of laps. Yet even the world’s brightest engineers struggled to solve the chronic issue of lag at lower revs, which could be as long as two in motorsport seconds according to drivers of the time.

Ferrari is believed to have been the first team in F1 to experiment with an anti-lag system – injecting fuel directly into the turbine section of the turbo – though the team’s 1982 and 1983 constructors’ titles owed more to the 126C’s strong aero and chassis.

In world rallying, Saab’s 99 Turbo was winning rallies before Audi’s fivecylinder turbo Quattro started the all-wheel drive revolution – though the Ingolstadt brand was first to employ anti-lag techniques. Like Ferrari, it squirted petrol into the turbo to keep it spinning on the overrun.

Turbos were banned from F1 after 1988 on safety grounds, and WRC’s glorious Group B era was abruptly ended by a series of fatalities.

Rallying has persisted with the turbo formula, and today’s WRC contenders rely on the anti-lag systems.

Just keep spinning

How it works

1 OLD VS NEW

F1 turbo engines forced drivers to use throttle early to anticipate lag, while in rallying drivers such as Walter Rohrl would left-foot brake – using the right to keep on the gas. In the WRC, the latter technique is no longer necessary with the sophisticated anti-lag systems – which help overcome turbo restrictors that limit air flow into the turbo.

2 FRESH AIR

The Engine Control Unit has always played a pivotal role in an anti-lag system. With an inletbypass – or secondary air injection – system, the car’s brain detects when the driver has come off the gas and closed the throttle valve. It then opens a solenoid valve in the bypass valve, allowing air to bypass the engine and flow directly into the exhaust manifold.

3 RICH MIX

With the cylinders deprived of their usual dose of air, the ECU next instructs the fuel injectors to spray extra petrol into the chamber to create a rich (low air, high fuel) mixture. The fuel that can’t be burned during the combustion process is spewed into the exhaust manifold, meeting with the bypassed air and exploding on contact with the hot plumbing.

4 BIG DRINKERS

The process used to severely limit the life of components but it seems improvements in computing power and component materials have helped to make ALS a more viable proposition for road cars. Not necessarily fuel, though – and Ford has already admitted it sacrificed consumption for the benefit of the GT’s throttle response.

5 BLADE RUNNER

Occurring conveniently before the turbine blades, the resulting kinetic energy helps to keep them spinning – and shortening the time it takes for the turbo to get back into its boost threshold. Result: instantaneous throttle response.