Are you having issues with slow turbo spool and significant turbo lag in your engine, or do you just want to understand what it means?
Then you’re in the right place. I’ve dealt with this issue multiple times when I tried to reduce turbo lag on my own drift cars.
When there’s nothing wrong with the engine, achieving faster spool and reducing turbo lag can often be very expensive and time-consuming.
In this article, I’ll explain what turbo lag is and how you can reduce it with a few simple steps from home.
What is Turbo Lag?
Turbo lag is the delay between pressing the accelerator pedal and opening the throttle valve until the turbocharger starts providing boost pressure and increasing power. This is also known as spool-up time. Gasoline engines often have longer turbo lag than diesel engines, and larger engines with smaller turbochargers have shorter turbo lag than small engines with large turbochargers.
For example, a small gasoline 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, the turbo lag is the time it takes to reach 4500 RPM, i.e., full power.
Modern turbocharged cars are often designed to have turbo lag that is practically non-existent, especially 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. Turbo lag is often reduced by a twin-turbo setup. You can also use a supercharger to reduce 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 having some knowledge before attempting it.
Causes of Slow Spool / Turbo Lag
So, if you have a standard or slightly tuned engine and your engine suddenly has slower turbo spool and increased turbo lag, there are common causes you should look into to diagnose the problem. Here are some of the most frequent causes of slow turbo spool and increased turbo lag.
Boost Leak / Exhaust Leak
A boost or exhaust leak is the most common issue regarding turbo lag. Exhaust leaks are affected when the 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 boost pressure leaks.
Faulty Wastegate
A faulty wastegate or wastegate vacuum or pressure hoses can also increase turbo lag and reduce your engine’s performance. Check and ensure that the wastegate control rod is properly installed and that the rod and wastegate move without any issues. Also, check the wastegate hoses. You can use vacuum or pressure to see if the wastegate is leaking and if the control arm is in good condition.
Bad Turbo Boost Pressure Solenoid
The boost pressure solenoid regulates and controls the pressure or vacuum to the wastegate. If the boost solenoid is faulty, it may not be able to control the wastegate properly, leading to increased turbo lag and slower turbo spool. You can use a multimeter to measure and check that the boost solenoid is in good condition.
Turbo Boost Pressure Sensor
If the boost pressure sensor is faulty, it can send incorrect information to the engine control unit, which may result in 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
Internal parts such as the exhaust wheel can be damaged and in such cases cause turbo lag. Remove the exhaust and boost pipes around the turbocharger to check the condition of the turbo’s turbine. If you have a supercharger with turbo lag, check the supercharger belt and look for other intake leaks.
Faulty Camshaft Timing
Incorrect camshaft timing can be due to an ill-fitting replacement timing belt or, in fact, a worn belt. Check the camshaft timing and ensure that the gears haven’t moved. Align them with the standard TDC markings. You can often find this information on various car forums where you can learn how to align the camshafts for your engine.
Wrong Turbo for the Engine
If you’ve replaced the turbocharger on your engine, you may have installed a larger turbocharger; this can also lead to increased turbo lag. Make sure the turbocharger is original and the correct one for your car model. If you’ve replaced it with a larger one, it might be a bit too big, and you’ll probably have to live with the turbo lag. In this case, read further in the article for tips on how to reduce turbo lag.
Incorrect Ignition Timing
Incorrect ignition timing can also cause turbo lag. It can be quite difficult to detect if you have bad ignition timing on modern engines. Modern engines are not capable of adjusting ignition timing. Therefore, check for any error codes and ensure that the knock sensors are in order. If you have an older engine with adjustable ignition timing, use a timing light to ensure 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 faulty sensor such as the MAF, engine coolant temperature sensor, O2 sensor, or MAP sensor.
What is Turbo Spool Time?
So, what’s the difference between turbo lag and turbo spool time? Well, as we’ve already discussed, turbo lag is the time between pressing the accelerator pedal and the turbo starting to spool. Turbo spool time is the time it takes for the turbocharger to spool up until the engine reaches full turbo pressure.
Turbo spool time is often confused and mixed up with turbo lag, but in reality, they are two completely different terms.
How to Reduce Turbo Lag
So, how do you actually want to reduce the turbo lag in your engine? These methods can be applied to both standard and modified engines. Here are some common actions you can take if you want to reduce your turbo lag.
Repair Faulty Parts
Before replacing any parts on your engine, make sure all turbo components are in good condition. Go through all the steps for the possible causes of turbo lag mentioned earlier in the article and ensure that all these parts are in good working order for your engine.
Re-tune the Engine
If you’re using an aftermarket control system such as Haltech for your car’s ignition and timing, there’s also a risk that your tuning is faulty and running with incorrect ignition timing or a lean mixture. This can lead to turbo lag. If you’re using a standard control system, these can often be re-tuned to achieve faster spool.
Adjust Camshaft Timing
If your engine has adjustable camshaft timing gears, you can often move them back and forth a few degrees. If you adjust them, you can often achieve faster spool. Note that if you adjust these and get faster spool, you’ll likely lose power at the highest RPM. If you have a standard engine, make sure the camshaft timing is correct and that the gears are properly aligned.
Get a Controller for the Turbo Boost Pressure Solenoid
By purchasing a better aftermarket controller for the wastegate solenoid, you can often reduce turbo lag a bit and ensure that the wastegate is properly closed during spool-up. This can often also be achieved by using a better wastegate or a stiffer spring inside the wastegate, but this also leads to increased turbo boost pressure at higher RPMs.
Replace the Turbocharger
If you’ve replaced your turbocharger and have severe turbo lag, you may have chosen the wrong turbo for your needs. Often, cheaper turbos have greater turbo lag, and if you want to reduce turbo lag, you should buy a more expensive one with twin-scroll, a smaller exhaust housing, ball bearings, and more sophisticated features. You can also replace it with a smaller turbocharger, but you’ll lose peak power if the turbocharger isn’t powerful enough to provide the required power. Holset is well-known for its powerful and fast-spooling turbochargers.
Anti-Lag Function
If you’re serious about your motorsport and really want to reduce turbo lag, you can set up an anti-lag function for your car if you have an aftermarket system. This is often done with an idle valve between the intake and before the throttle so that air always enters the engine, while retarding ignition and increasing fuel to allow the turbo to spin at low RPM. However, this causes damage and significantly increases turbocharger wear. So, only do this if you’re 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 better performance at lower speeds and with less lag. Superchargers have much better performance at low RPM, and these can often be used in combination with a turbocharger. However, it’s quite complex to run a turbocharger in combination with a supercharger, and you need some knowledge to make it work properly. You can also convert to a twin-turbo system to reduce turbo lag.
A turbocharger often gives you more power at higher RPMs, while a supercharger gives you more power at low RPM without turbo lag.