Turbochargers represent the promise of enhanced power, superior fuel efficiency, and improved engine performance. However, they also bring along an inherent trait known as ‘turbo lag’.
Turbo lag is the delay between applying throttle and the turbo producing boost pressure, and the engine providing meaningful power output.
This article aims to explain turbo lag, what causes it, the impact it has, and the ways you can mitigate it.
Turbochargers operate on the principle of forced induction. By compressing the air flowing into the engine, they allow for more fuel to be combusted in a shorter period, thereby enhancing the engine’s power output.
A turbocharger primarily comprises two components: a turbine and a compressor, connected by a shared axle.
The exhaust gases produced by the engine spin the turbine, which in turn spins the compressor, pushing more air into the engine’s combustion chambers.
A turbocharger is a very common way to increase power from a smaller sized engine, but not without a caveat – turbo lag.
What Is Turbo Lag
Turbo lag is the delay between the moment the accelerator pedal is depressed and when the turbocharger produces boost pressure and increased power output, causing a temporary lack of responsive acceleration.
The cause of this lag is the time taken for the exhaust system to generate enough pressure to drive the turbine (spool up), which then powers the compressor. The outcome is a noticeable delay in acceleration, which can affect the vehicle’s performance negatively.
Turbo lag is often most noticeable in driving scenarios where sudden acceleration is needed, such as overtaking or moving from a standstill. It can be identified as a delay between the moment you press the accelerator and when the vehicle noticeably accelerates.
What Causes Turbo Lag
In essence, turbo lag is a physics problem – it revolves around the principles of inertia and energy transfer.
Larger turbochargers with larger turbine and compressor masses have more inertia, making them slower to spool up.
Similarly, engines with lower RPMs or smaller sizes produce less exhaust energy, thus taking more time to get the turbocharger spinning.
Therefore, the size of the turbocharger and the characteristics of the engine both contribute to the extent of turbo lag.
How to Fix Turbo Lag
Several technological advancements have aimed to reduce turbo lag, such as those listed below.
Variable Geometry Turbos (VGTs)
Variable Geometry Turbo / Turbine (VGTs) change their turbine housing’s shape to improve exhaust energy utilisation, effectively reducing turbo lag.
The variable geometry turbine allows flexibility over the pressure ratio across the turbine. This flexibility can be used for improving low speed torque and reducing turbocharger lag, among other benefits.
Twin-turbo systems, either sequential or parallel, can use two turbochargers of different sizes to ensure optimal performance at varying RPMs.
The benefits to using a twin turbo setup is the ability to use differing sizes of turbochargers. The smaller turbocharger takes less time to spool up and works at lower RPM, whereas the larger turbo can provide higher boost pressure at higher RPM and exhaust flow.
Anti-Lag Systems (ALS)
Anti-lag systems are another advanced technology employed to combat turbo lag.
An anti-lag system typically consists of various different techniques used individually or together to reduce turbo lag, such as the following.
- Ignition retard, fuel dump, and throttle bypass
- Secondary air valves and inlets
- Turbo and intercooler bypass
- Nitrous oxide systems
- Electric turbochargers and MGU-H systems
Engine Design Changes
Several engine design changes can help reduce turbo lag, such as reducing intake and exhaust pipework diameter and length, increasing compression ratio, or increasing displacement.
Reducing intake air temperature also helps, this can be done by adding intercooler water spray kits, methanol injection, etc.
Turbo Lag vs Boost Threshold
It’s essential to distinguish turbo lag from the boost threshold, although they are often misunderstood or confused.
While turbo lag refers to the delay in turbo response, boost threshold is the minimum RPM at which a turbo can provide useful boost. It is more about the overall turbocharger and engine design rather than the response delay.
Modern vehicles have largely managed to minimize the impact of turbo lag through advanced engineering and design. Auto manufacturers strike a balance between power, efficiency, and turbo lag, ensuring a smooth and responsive driving experience.
Techniques like using smaller, twin-scroll turbochargers, or advanced electronics, have helped curb the effects of turbo lag significantly.
Turbo lag is an inherent trait of turbocharged engines. It has been a compelling challenge in automotive engineering, especially in the motorsport industry.
As technology and engineering continues to advance, the mitigation of turbo lag is improving, paving the way for more efficient and responsive turbocharged vehicles.