Are you having problems with a slow turbo spool and a lot of turbo lag on your engine, or just want to know what it means?
Then you are in the right place. I have dealt with this problem a lot of times when I have been trying to reduce the turbo lag myself on my drifting cars.
If everything is okay with the engine, get a faster spool and reduce the turbo lag can often be very costly and time-consuming.
In this article, I will learn you about what turbo lag is, and how you can reduce it with some simple steps from home.
What is turbo lag?
Turbo lag is the time delay of the time between when you are pressing the accelerator pedal and open the throttle body until the turbocharger is starting to deliver boost pressure and increased performance. This is also called Spool up time. Petrol/gas engines do often have more turbo lag than diesel engines, and larger engines with smaller turbochargers have a shorter amount of turbo lag than small engines with large turbochargers.
For an example, a small petrol engine with a pretty large turbo does not reach 1.5 bar before on 4500 rpm. If you are pressing the accelerator pedal and opening the throttle body on 2000 rpm, turbo lag is the time until you reach 4500 rpm and got full power.
Modern turbocharged cars are often designed to have a turbo lag which is almost non-existing, especially the diesel engines. But however, you can often feel it even on these engines if you are pushing the accelerator pedal on low rpms and you will notice that you won’t have any power for a period of time. Turbo lag is often reduced by a twin turbo setup. You can also use a supercharger to decrease the turbo lag.
Superchargers do almost have no turbo lag and they can be combined with a turbocharger. However this process is pretty difficult to make it work properly, so I recommend you to have some knowledge before trying this.
Causes of slow turbo spool/turbo lag
So if you have a standard or a lightly tuned engine and your engine suddenly got slower turbo lag and increased turbo lag, there are some common causes that you should look for to diagnose the problem. Here are some of the most common causes of slow turbo spool and increased turbo lag.
Boost Leak / Exhaust leak
A boost leak or an exhaust leak is the most common problem when it comes to turbo lag. Exhaust leaks are affected if the exhaust leak is at the manifold before the turbocharger. If the exhaust leak is further back on the exhaust pipe, the turbo spool should not be affected. Boost leaks will almost in all cases cause an increased turbo lag. Pressure test your intake system with compressed air or use an EVAP smoke machine to find any possible boost pressure leaks.
A faulty wastegate or wastegate vacuum/pressure hoses can also increase the turbo lag and lower the power in your engine. Check and make sure that the wastegate control rod is correctly installed and make sure that the rod and the wastegate are moving without issues. Also, check the hoses to the wastegate, you can use vacuum or pressure to see if there is any leaks of the wastegate and that the control arm is in good shape.
Bad Turbo boost Pressure Solenoid Valve
The boost pressure solenoid is regulating and controlling the pressure or vacuum to the wastegate. If the boost pressure solenoid valve is faulty, it may not control the wastegate correctly, which means increased turbo lag and increased turbo spool time. You can use a multimeter to measure and test if the boost pressure solenoid valve is in good shape.
Turbo boost pressure sensor
If the boost pressure sensor is faulty, it may send wrong information to the engine control unit, which may result in an increased turbo lag time. You can use an OBD2 scanner to check the boost pressure sensor signal pressure for the most standard cars.
Broken turbocharger or supercharger
The internal parts like the exhaust impeller can be damaged and in this case cause turbo lag. Remove the exhausts 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 for the supercharger and check for other intake leaks.
Faulty camshaft timing
A faulty camshaft timing can be caused by an incorrectly timing belt replacement or a worn out timing belt. Check the camshaft timing and make sure that the gears have not moved. Line them up with the standard TDC marks. You can often find this information on different car forums of how to line up the camshafts for your engine.
Wrong turbo of the engine
If you have replaced the turbocharger on your engine, you have maybe also fitted a larger turbocharger, this can also cause an increased turbo lag. Make sure that the turbocharger is original and the right turbocharger for your car model. If you have replaced it with a larger one, it may be a bit too large and you do probably have to live with the turbo lag. In this case, go further down in the article to learn some tips on how to reduce the turbo lag.
Faulty ignition timing
Faulty ignition timing can also cause turbo lag. This can be pretty difficult to know if you have wrong ignition timing on modern engines. Modern engines does not have the ability to adjust the ignition timing on. In this case, check for any trouble codes and make sure that the knock sensors are okay. If you are having a older engine with adjustable timing, make sure that the timing is correct with a timing light.
Lean air/fuel mixture
Lean air/fuel mixture can cause increased turbo lag. a lean mixture is often caused by boost leaks or intake leaks mentioned before. But it can also be caused by a faulty sensor like the MAF, engine coolant temperature sensor, O2 sensor or a MAP sensor.
What is turbo spool time?
So what’s the difference between turbo lag and turbo spool time? Well as we discussed before, turbo lag is the time between you are pressing the accelerator pedal until the turbo starts spooling up. Turbo spool time is the time it takes for you turbocharger from it starts spooling up until the engine reaches the full turbo pressure.
Turbo spool time can often be confused and mixed with the turbo lag, but they are actually two completely different terms.
How to reduce the turbo lag?
So how are you actually reducing your turbo lag on your engine? These methods can both be made on standard and modified engines. Here are some common things to do if you want to reduce your turbo lag.
Repair faulty parts
Before you are replacing any parts on your engine. Make sure that all turbo parts are in good shape. Go through all steps on the earlier possible causes of turbo lag in the article and make sure that all these parts are in good shape for your engine.
Retune the engine
If you are using an aftermarket control system like Haltech for your timing and ignition on your car, there is also a risk that your tune-up is faulty and running with a faulty ignition timing or lean mixture. This can cause a turbo lag. If you are using a standard control system, they can often be re-tuned to get a faster spool up also.
Mix with the camshaft timing
If your engine is upgraded with adjustable camshaft timing gears, you can often move them a few degrees in advance and retard. By adjusting these, you can often get a faster spool up. Not that if you mix with these and get a faster spool up, you will probably lose performance at the top peak RPM. If you have a standard engine, make sure that the camshaft timing is good and the gears are not lined up.
Get a controller for the turbo boost pressure solenoid
By purchasing a better aftermarket controller for the wastegate solenoid you can often reduce the turbo lag a bit of making sure that the wastegate is properly closed during the spool up. This can also often be fixed with a better wastegate or a harder spring inside the wastegate, but this will also cause an increased turbo boost pressure on higher rpm.
Replace the turbocharger
If you have replaced your turbocharger and you got a lot of turbo lag, you might have chosen the wrong turbo for you. Often cheaper turbo’s do have more turbo lag and if you want to reduce the lag, you might want to get a more expensive one with twin scroll, smaller exhaust house, ball bearing and more fancy functions. You can also replace it with a smaller turbocharger, but you will loose top power if the turbocharger is not enough for the required horsepower output. Holset is known for having high performance and fast spooling turbochargers.
If you are serious about your motorsport and really want to reduce the turbo lag, you can set up an anti-lag function for your car if you have an aftermarket control system. This is often made with an idle valve between the intake and before the throttle body to always get air into the engine when at the same time retarding the ignition and increasing the fuel to get the turbo spooling at lower rpm. However, this will cause damages and increase the wear on the turbocharger a lot, so only do this if you are serious about your motorsport or have the money to repair your engine at all the time.
Turbocharger vs Supercharger
A supercharger is often used on modern cars to get a higher performance at lower rpm and low amount of lag. Superchargers do have a lot better low rpm performance and these can often be used in combination with a turbocharger. However to get a turbocharger to function together with a supercharger, is pretty complexed and you need to have some knowledge to get this working properly. You can also convert to a twin-turbo setup to get reduced turbo lag.
A turbocharger is often giving you a higher performance on higher rpm, while a supercharger is giving you more low rpm power without the turbo lag.