Most rally fans know the hallmark sound of an anti-lag system. First used in Formula 1 in the 1980s, anti-lag systems are designed to keep a turbocharger spinning while off throttle. Most systems produce a loud “pop,” often accompanied by visible flames. Though some owners of modified cars will tolerate the occasional fireball, a new Turbo S owner might find this trait unappealing. From an environmental perspective introducing additional unburned fuel outside the combustion chamber is also less than ideal. Between the added noise and constantly needing to wipe soot and scorch marks off the rear bumpers, a fuel-driven anti-lag is not well suited to a modern high-end performance car. In order to maintain boost while off-throttle Porsche has come up with a different solution.
Maintaining Boost Without Adding Fuel
Per Engineering Explained, the Porsche system sets itself apart from traditional anti-lag by not requiring additional fuel to maintain boost. No extra fuel, no fireballs. The so-called Dynamic Boost system instead uses the electronic throttle body to maintain airflow through the engine. Normally when the throttle pedal is released the throttle butterfly closes fully. Porsche’s system opens the throttle butterfly partially, maintaining some boost pressure in the intake and facilitating airflow through the engine.
This additional airflow has two primary functions. The first, and most obvious, is to facilitate spinning the turbochargers. This aids in maintaining boost pressure when off throttle. The second is to keep the intake manifold from becoming an area of negative pressure. The latter component aids in throttle response, which is valuable in a heavily turbocharged engine.
The system does have one notable downside; with the Dynamic Boost system the effect of engine braking is dramatically reduced. Remember, the system’s goal is to flow air through the engine, which effectively negates compression braking. The effect is most noticeable with the car in Sport and Sport+ modes, when the car is less likely to rely on compression braking. In situations where the effect is most pronounced the driver will primarily use the brakes to slow the car anyways.
In the interest of disclosure, Porsche is not the only manufacturer to come up with this solution. Ford also holds a patent for a similar system. Several of the traditional anti-lag methods, including the D-Valve method and inlet bypass share some similarities with both the Porsche and Ford systems. These competition-proven do still rely on adding unburned fuel into the system, and lack the necessary sophistication and clean burn required for a street car.