Editing Turbocharger (section)

== Turbo lag and boost threshold {{anchor|Turbocharger lag|Lag}} ==
{{refimprove section|date=June 2022}}

'''Turbo lag''' refers to delay{{snd}}when the engine rpm is within the turbocharger's operating range{{snd}}that occurs between pressing the throttle and the turbocharger spooling up to provide boost pressure.<ref>{{cite web |title=What Is Turbo Lag? And How Do You Get Rid Of It? |url=https://www.motortrend.com/how-to/what-is-turbo-lag-how-do-you-get-rid-of-it/ |website=www.MotorTrend.com |access-date=12 June 2022 |language=en |date=7 March 2015}}</ref><ref>{{cite web |title=Turbo Lag. Reasons For Turbocharger Lag. How To Fix Turbo Lag |url=https://carbuzz.com/car-advice/what-is-turbo-lag |website=www.CarBuzz.com |access-date=12 June 2022 |language=en-us |date=25 September 2021}}</ref> This delay is due to the increasing exhaust gas flow (after the throttle is suddenly opened) taking time to spin up the turbine to speeds where boost is produced.<ref>{{cite web |title=What is turbo lag? |url=http://www.enginebasics.com/Advanced%20Engine%20Tuning/Turbo%20Lag.html |website=www.enginebasics.com |access-date=12 June 2022}}</ref> The effect of turbo lag is reduced [[throttle response]], in the form of a delay in the power delivery.<ref>{{cite web |title=5 Ways To Reduce Turbo Lag |url=https://www.carthrottle.com/post/how-can-you-reduce-turbo-lag/ |website=www.CarThrottle.com |date=19 July 2016 |access-date=12 June 2022 |language=en}}</ref> Superchargers do not suffer from turbo lag because the compressor mechanism is driven directly by the engine.

Methods to reduce turbo lag include:{{citation needed|date=June 2022}}
* Lowering the rotational inertia of the turbocharger by using lower radius parts and ceramic and other lighter materials
* Changing the turbine's ''[[aspect ratio]] (A/R ratio)''
* Increasing upper-deck air pressure (compressor discharge) and improving wastegate response
* Reducing bearing frictional losses, e.g., using a [[foil bearing]] rather than a conventional oil bearing
* Using [[Variable-geometry turbocharger|variable-nozzle]] or [[#Twin-scroll|twin-scroll]] turbochargers
* Decreasing the volume of the upper-deck piping
* Using multiple turbochargers sequentially or in parallel
* Using an [[antilag system]]
* Using a turbocharger spool valve to increase exhaust gas flow speed to the (twin-scroll) turbine
* Using a [[butterfly valve]] to force exhaust gas through a smaller passage in the turbo inlet
* Electric turbochargers<ref name=parkhurst>{{cite web|last=Parkhurst |first=Terry |title=Turbochargers: an interview with Garrett's Martin Verschoor |date=10 November 2006 |publisher=Allpar |url =http://www.acarplace.com/cars/turbochargers.html |access-date=12 December 2006}}</ref> and [[hybrid turbocharger]]s.

A similar phenomenon that is often mistaken for turbo lag is the '''boost threshold'''. This is where the engine speed (rpm) is currently below the operating range of the turbocharger system, therefore the engine is unable to produce significant boost. At low rpm, the exhaust gas flow rate is unable to spin the turbine sufficiently.

The boost threshold causes delays in the power delivery at low rpm (since the unboosted engine must accelerate the vehicle to increase the rpm above the boost threshold), while turbo lag causes delay in the power delivery at higher rpm.