What is Turbo Lag & Turbo Spool? – Meaning, Causes & Solutions

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Do you have problems with a slow turbo spool and a lot of turbo lag on your engine, or do you just want to know what that means?

Then you have come to the right place. I have dealt with this problem many times when I myself tried to reduce the turbo lag on my drifting cars.

When there is nothing wrong with the engine, getting a faster spool and reducing the turbo lag can often be very costly and time-consuming.

In this article, I will explain what a turbo lag is and how you can reduce it with a few simple steps from home.

What is turbo lag?

Turbo lag is the time delay between pressing the accelerator pedal and opening the throttle valve until the turbocharger starts to deliver boost pressure and increase power. This is also known as the wind-up time. Gasoline engines often have a longer turbo lag than diesel engines, and larger engines with smaller turbochargers have a shorter turbo lag than small engines with large turbochargers.


For example, a small petrol engine with a fairly large turbocharger only reaches 1.5 bar at 4500 rpm. If you press the accelerator pedal and open the throttle body at 2000 rpm, turbo lag is the time it takes to reach 4500 rpm, i.e. full power.

Modern turbocharged cars are often designed to have a turbo lag that is virtually non-existent, especially the diesel engines. But even with these engines you can often feel that when you press the accelerator pedal at low RPM, you have no power for a while. The turbo lag is often reduced by a double turbo set-up. You can also use a supercharger to reduce the turbo lag.

Superchargers have almost no turbo lag and can be combined with a turbocharger. However, this procedure is quite difficult to get right, so I recommend that you have some knowledge before you try this.

Causes of slow turbo spool/turbo lag

Turbo Lag

So if you have a standard or a lightly tuned engine and your engine suddenly has a slower turbo spool and a higher turbo lag, there are some common causes that you should look for to diagnose the problem. Here are some of the common causes of slow turbo spool and increased turbo lag.

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Boost Leak / Exhaust leak

A boost or exhaust leak is the most common problem when it comes to turbo lag. Exhaust leaks are affected when the exhaust leak is located at the manifold in front of the turbocharger. If the exhaust gas leak is further back on the exhaust pipe, the turbo spool should not be affected. Boost leaks cause increased turbo lag in almost all cases. Test your intake system with compressed air or use an EVAP smoke machine to find any possible boost pressure leaks.

Faulty Wastegate


A defective wastegate or wastegate vacuum or pressure hoses can also increase turbo lag and reduce the performance of your engine. Check and make sure that the wastegate control rod is installed correctly and make sure that the rod and wastegate move without any problems. Also, check the hoses to the wastegate. You can use a vacuum or pressure to see if the wastegate is leaking and if the control arm is in good condition.

Bad Turbo Boost Pressure Solenoid Valve

The boost pressure solenoid regulates and controls the pressure or vacuum to the wastegate. If the boost solenoid valve is defective, it may not be able to control the wastegate correctly, resulting in increased turbo lag and increased turbo spool. You can use a multimeter to measure and check that the boost solenoid valve is in good condition.

Turbo boost pressure sensor

If the boost pressure sensor is defective, it can send incorrect information to the engine control unit, which can lead to increased turbo lag. You can use an OBD2 scanner to check the signal pressure of the boost pressure sensor for most standard cars.

Broken turbocharger or supercharger

The internal parts such as the exhaust impeller can be damaged and in this case cause turbo lag. Remove the exhaust and boost pipes around the turbocharger to check the shape of the turbo impeller. If you have a supercharger with turbo lag, check the belt of the supercharger and check for other intake leaks.

Faulty camshaft timing

Incorrect camshaft timing can be caused by an unsuitable replacement timing belt, or, indeed, a worn one. Check the camshaft timing and make sure that the gears have not moved. Align them with the standard TDC markings. You can often find this information in various car forums where you can learn how to align the camshafts for your engine.

Wrong turbo for the engine

If you have replaced the turbocharger on your engine, you may have installed a larger turbocharger; this can also lead to increased turbo lag. Make sure that the turbocharger is original and the correct turbocharger for your car model. If you have replaced it with a larger one, it may be a bit too large and you will probably have to live with the turbo lag. In this case, go further down the article for some tips on how to reduce turbo lag.

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Incorrect ignition timing

Incorrect ignition timing can also cause turbo lag. It can be quite difficult to detect if you have the wrong ignition timing on modern engines. Modern engines are not capable of adjusting the ignition timing. Therefore, check for possible error codes and make sure that the knock sensors are in order. If you have an older engine with adjustable ignition timing, use an ignition timing light to make sure that the ignition timing is correct.

Lean air-fuel mixture

A lean air-fuel mixture can cause increased turbo lag. A lean mixture is often caused by the aforementioned boost or intake leaks. It can also be caused by a defective sensor like the MAF, engine coolant temperature sensor, O2 sensor, or MAP sensor.

What is turbo spool time?

So what is the difference between turbo lag and turbo spool time? Well, as we have already discussed, turbo lag is the time between pressing the accelerator pedal and the start of turbo spooling. Turbo spool time is the time it takes for the turbocharger to charge until the engine reaches full turbo pressure.

The turbo spool time can often be confused and mixed up with the turbo lag, but actually they are two completely different terms.

How to reduce the turbo lag

So how do you actually reduce the turbo lag of your engine? These methods can be applied to both standard and modified engines. Here are some common things you can do if you want to reduce your turbo lag.

Repair faulty parts

Before you replace any parts on your engine, make sure that all turbo parts are in good condition. Go through all the steps for the previous possible causes of turbo lag in the article and make sure that all these parts are in good condition for your engine.

Re-tune the engine

If you use an aftermarket control system such as Haltech for the ignition timing and ignition of your car, there is also a risk that your tuning is faulty and runs with an incorrect ignition timing or lean mixture. This can lead to turbo lag. If you are using a standard control system, these can often be re-tuned to achieve a faster spool.

Mix with the camshaft timing

If your engine is retrofitted with adjustable camshaft timing gears, you can often move them back and forth a few degrees. If you adjust them, you can often achieve a faster rewind. Note that if you mix them with these and get a faster spool, you will probably lose power at the highest RPM. If you have a standard engine, make sure the camshaft timing is good and the gears are not lined up.

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Get a controller for the turbo boost pressure solenoid

By purchasing a better aftermarket controller for the wastegate solenoid valve, you can often reduce the turbo lag a little and ensure that the wastegate is properly closed during the spool up. This can often also be achieved by using a better wastegate or a harder spring inside the wastegate, but this also leads to increased turbocharging pressure at higher RPMs.

Replace the turbocharger

If you have replaced your turbocharger and have a severe turbo lag, you may have chosen the wrong turbo for you. Often cheaper turbos have a larger turbo lag, and if you want to reduce the turbo lag, you should buy a more expensive one with a twin-screw, smaller exhaust housing, ball bearings, and more fancy features. You can also replace it with a smaller turbocharger, but you will lose peak power if the turbocharger is not powerful enough to deliver the required power. Holset is well known for its powerful and fast spooling turbochargers.

Anti-lag function

If you are serious about your motorsport and you really want to reduce turbo lag, you can set up an anti-lag function for your car if you have a retrofit system. This is often done with an idle valve between the intake and in front of the throttle so that air is always entering the engine, while at the same time delaying ignition and increasing fuel to allow the turbo to spin at lower revs. However, this causes damage and increases the wear and tear of the turbocharger considerably. So only do this if you are serious about your motorsport or have the money to keep repairing your engine.

Turbocharger vs Supercharger


A supercharger is often used in modern cars to achieve higher performance at lower speeds and with less deceleration. Superchargers have much better performance at low revs, and these can often be used in combination with a turbocharger. However, it is quite complex to make a turbocharger work in combination with a supercharger, and you need some knowledge to make it work properly. You can also convert to a dual turbo system to reduce the turbo lag.

A turbocharger often gives you more power at higher RPMs, while a supercharger gives you more power at low RPMs without turbo lag.

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