Volumetric Efficiency Of Turbocharged Engines — An Essential Overview

When seeking greater performance from a turbocharged engine, you can make certain adjustments to the turbo and ancillaries. However, you may need to pay particular attention to how the engine breathes. To do this, you should understand the volumetric efficiency (VE) concept: how well the motor can transport liquid or gas based on its size. So, what do you need to know about the volumetric efficiency of turbocharged engines?

What is the volumetric efficiency of an engine?

To calculate an engine's volumetric efficiency and work out how much air and fuel your engine should move at a certain RPM (revs per minute), you need to measure the airflow at that RPM based on the engine’s size (or displacement). 

With this data, you'll be able to calculate how much the engine should be pumping at that speed compared to what is actually entering the combustion chamber. 

If the vehicle has a low reading regarding the engine’s volumetric efficiency, there could be several causes. For example, if the oxygen sensor is lean while the throttle is wide open, this could be due to faulty air metering. Alternatively, you may have an issue with the fuel rail system or injectors if the oxygen sensor is lean while you have a good volumetric efficiency number. You could make improvements if you replace the standard rail and injectors.

Understanding where the turbochargers come in

So, what is the volumetric efficiency of an engine when turbocharged? Turbochargers can make a considerable difference in these calculations. After all, the air will be forced into the engine, immediately improving performance compared to a standard motor. 

Additional data is needed to set new performance targets. Here, the technician will need to know the boost pressure and the incoming air temperature. Remember, the temperature can be reduced if you have an intercooler fitted. One of the primary differences between a standard and a turbocharged engine is that the technician will need to use boosted pressure rather than typical air pressure when setting target performance figures.

Boost leaks

If the vehicle has a boost leak, some of the “expected” air will have been forced out through that leak instead. The engine management system will overcompensate as the air entering the turbocharger has to go through the MAF (mass air flow) sensor — which regulates how much fuel is sent in. This will lead to a much higher VE calculation, as the system “thinks” it is getting more air, so it supplies more fuel.

Faulty MAF sensors

If the MAF sensor is faulty, it may not accurately measure the air entering the turbocharger while reporting an incorrect value to the management system. In this case, the VE measurement would be lower than normal. Replace the MAF sensor to compensate.

Exhaust problems

Remember that problems can arise on the outlet side as well. In this case, some exhaust restrictions can lead to a blockage, slowing down the turbocharger. This will affect performance targets as the engine will not be able to breathe correctly. The engine will still get the correct amount of fuel via the sensor, but you will need to address the exhaust restriction first before you can see if there are any other input issues.

Diagnosing issues

A skilled technician can analyse the results of any VE calculation and have a good idea of where to turn to make adjustments. For example, when the results indicate a possible problem with air metering, they might look closely at the ducting mechanism between the MAF sensor and the turbocharger’s air inlet. Talk with your parts supplier so you can replace the faulty parts.

Following the process of elimination

There are many potential setup faults or technical problems, and each one could lead to a separate VE calculation. The technician may need to consider the existence of more than one problem at a time and, in this case, may have to go through a step-by-step process of elimination. Still, measuring an engine’s volumetric efficiency is a great way to shortcut the entire process and can be as important as a separate dyno tune-up.

Choosing the correct parts after calculating the volumetric efficiency of turbocharged engines  

As your technician calculates the volumetric efficiency of your turbocharged engine, they may discover faulty components. In this case, you will need some high-quality parts that you can buy from Car Mods Australia, where we stock more than 250,000 products from more than 200 world-recognised brands.

Buying parts from the experts

We invite you to check out our engine, exhaust and cooling products to help you hit those ideal performance targets. We can also help you with brakes and drivetrains, suspension and interior and exterior parts. So, reach out to Car Mods Australia today. Our dedicated and enthusiastic staff members will be keen to help you.