What is Turbo Lag?

Jessica Shea Choksey | Aug 23, 2021

Turbocharging is one of the most common ways to increase an engine’s power output. Many car manufacturers design vehicles with turbocharged engines to offer consumers greater performance, higher efficiency, and lower emissions over models with normally aspirated engines. In the same way, car enthusiasts often add aftermarket turbochargers to give their vehicles an extra boost of power in everyday driving. Although there are tangible benefits to turbocharging engines, there is one real downside: turbo lag.

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How Does a Turbocharger Work?

Before defining turbo lag, it is first necessary to understand how a turbocharger works. All internal combustion engines (ICE) rely on air to burn fuel. A turbo is a turbine-driven device that spins from exhaust gas pressure created by the engine, forcing extra compressed air into the engine’s combustion chamber. That excess air allows the ICE to burn proportionately more fuel in the same amount of time, increasing a vehicle’s horsepower and torque.

What is Turbo Lag?

Turbo lag is the time it takes to feel the extra rush of power after pushing down on the accelerator pedal and opening the throttle. Instead of undergoing an immediate surge in forward thrust, the vehicle will appear unresponsive for a moment before it begins to accelerate more briskly.

This delay is due to the time it takes for the turbo to spin fast enough to force extra compressed air into the combustion chamber. Most turbochargers spin 80,000 to 100,000 revolutions per minute (rpm). Reaching that spin speed may take anywhere from a fraction of a second to a couple of seconds, which is a long enough duration for the driver to feel the “lag” before experiencing an influx of power.

Because a turbocharger generally matches up to a specific mid-level rpm range to function optimally, turbo lag is more noticeable in low-rpm driving. It can become a cause for concern when a driving situation requires quick changes in power. In some cases, turbo lag can impede a driver’s ability to make an effective freeway overtaking maneuver or a similar move requiring immediate acceleration.

Turbo Lag vs. Boost Threshold

On a turbocharged engine, two concepts are often mistaken for one another: turbo lag and boost threshold. While turbo lag refers to the time gap between the point when the gas pedal is mashed to when the turbo spools up and feeds air into the engine, the boost threshold is the minimum engine speed needed to create enough exhaust gas pressure to spin the turbo.

For turbo lag to occur, the engine must first cross the boost threshold. The engine generally reaches its boost threshold in normal mid-range driving—between 2500 and 4000 rpm—before the driver seeks turbo power. Without reaching the boost threshold, turbo lag is a moot point. Since the two events are independent of one another, and there is no overlap, the boost threshold is not a component of the turbo lag equation.

Reducing Turbo Lag

Although there is no surefire way to eliminate turbo lag, there are several mechanical solutions and modifications that can help reduce its effects:

  • Replace the stock factory exhaust system with a free-flow unit to minimize engine backpressure and allow the turbo to spool more quickly
  • Install a high-performance intake system to increase airflow to the turbocharger
  • Optimize air-fuel ratios with an engine control unit tune-up
  • Replace the factory blow-off valve with a sturdier aftermarket unit
  • Add a wastegate to bleed off excess exhaust pressure at high engine rpm
  • Consider sequential turbocharging; adding a second turbocharger to work alongside the first unit to widen the engine’s power band, although this can be a very costly option
  • Add nitrous oxide to increase exhaust pressure, but this is considered an extreme approach that can have negative results such as excessive backfiring or even engine damage if the fuel to air ratio is incorrect

Summary

For those who own vehicles with turbocharged engines, turbo lag is part of the everyday driving experience. Although there are ways to lessen its effects, most drivers grow accustomed to turbo lag over time. Test driving a vehicle will help determine if a turbocharged offering is the right choice for a car buyer.

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