How Much HP Does a Turbo Add? . Turbochargers are a valuable asset for enhancing torque output and fuel efficiency. Diesel engines, in particular, benefit from the device as it supplies denser air to aid with the compression. How much horsepower does a turbocharger add? It depends on various factors, but the impact is rarely negligible.
Turbos have been around for decades, and ever since their mass adoption, their usage has been growing steadily. Implementing better fuel economy and reduced emissions has recently broadened the use case for a turbocharger.
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What Are Turbochargers?
Turbochargers are a type of forced induction system that compresses the air flowing into the car’s engine. The advantage of compressing the air is that it lets the engine squeeze more air into a cylinder, and more air means that more fuel can be added. Therefore, you get more power from each explosion in each cylinder.
A turbocharged engine produces more power overall than the same size engine without the charging. This can significantly improve the power-to-weight ratio for the engine. This also means that a smaller engine can produce higher horsepower more efficiently, which means fewer stops at the gas station.
In order to achieve this boost, the turbocharger uses the exhaust flow from the engine to spin a turbine, which in turn spins an air pump. The turbine in the turbocharger usually spins at speeds between 80,000 and 200,000 rotations per minute (rpm) — that’s up to 30 times faster than most car engines can go. And since it is hooked up to the exhaust, the turbine also runs at very high temperatures.
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How Much Horsepower Does a Turbocharger Add?
You have to consider several factors when determining the power gain from turbocharger use in a motor.
A turbocharger may typically increase an engine’s horsepower by anywhere between 40 and 300 horsepower.
However, the exact number is difficult to tell as the quality of collaboration of different parts always influences the overall improvement.
Still, by considering these factors, we may get to a number that’s in the vicinity of the actual impact.
Here are the factors that influence how much HP does a turbo add:
Turbocharger size
Smaller turbos tend to spool up quickly, which makes them good for delivering a boost at lower RPMs. This is advantageous for achieving instant throttle response, and it’s more utilized in petrol engines.
The larger the turbo, the more airflow it can create and boost the pressure in the combustion process. In short, a bigger turbocharger size means greater power gains.
In horsepower terms, a bigger turbocharger has a greater capacity to increase the engine’s horsepower as it can burn more fuel. The increase in HP from a bigger turbo can go over 30% above the engine’s basic output.
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Turbocharger design
Along with the size, the turbocharger design is one of the biggest factors influencing the engine’s HP. Turbocharger dealers claim different turbo
designs deliver varying levels of performance and efficiency. High-performance turbos can deliver increased air pressure and consequently boost the pressure in the combustion chamber.
If a component like a compressor or a turbine mismatches relative to the demands of the other components, the turbocharger will have a limited airflow.
A smaller compressor will struggle to provide sufficient air intake to match the capacity of a larger turbine. That the turbine is capable of handling a greater volume of exhaust gases will make no difference, and the airflow will still be limited.
That’s why the components need to be compatible with each other’s capacities and have matching performances.
Boost pressure limitations of the engine
The turbocharger may well be able to boost the engine’s power output, but the engine may not possess the capacity to handle it.
The engine’s design and components can limit its capacity to receive added power. At the very least, having such limitations can put it in danger of breaking down.
Here are the factors to consider when discussing the engine’s limitations to withstand additional HP from the turbocharger:
Quality of components
Pistons, connecting rods, cylinder heads, etc., need to endure the increased stress that comes with higher boost pressures. Boosting the engine beyond its capacity to withstand the added horsepower can lead to failure.
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Tuning
The ECU is responsible for managing various parameters like the air-fuel mixture and timing. Having suboptimal tuning will limit the engine’s capacity to accept the added boost, but it can also work under more stress than intended.
When it comes to boosting pressure, tuning helps establish safe and effective limits for the engine.
Fuel quality
Using fuel that’s of lower octane than the recommended ratings can lead to pre-ignition and, consequently, engine damage. Pre-ignition is an occurrence in petrol engines, and it means that the air-fuel mixture had ignited prior to the occurrence of the ignition spark.
This malfunction can happen because of high temperatures, pressures, or hot spots in the combustion chamber. Low-octane fuel and suboptimal timing can also contribute to pre-ignition.
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Engine displacement
When it comes to the amount of impact on the engine’s horsepower, what also matters is the size of the engine. A smaller engine will experience larger power gains compared to other engines.
Engine displacement refers to the total volume that all the cylinders can sweep in a single motion. Larger displacement engines allow for more fuel to be mixed with compressed air, and as a result, they produce more power.
When it comes to turbochargers, smaller displacement engines get a bigger boost because their power output is small. Technological advances, especially those related to turbochargers, have enabled weaker engines to produce a significant amount of power without sacrificing the vehicle’s economy.
Intercooling
The intercooling process enhances the efficiency and, with that, the engine’s power output. Its main function is to ensure that the air-fuel mixture is denser and contains more oxygen molecules. This is made possible through a cooling process that removes the heat that’s generated during the compression of the intake air from the environment.
As devices, intercoolers are located between the compressor and the engine’s intake manifold. They’re not an inherent part of the turbocharger, nor are they directly integrated with the engine, but rather, it’s a component that helps the process.
The turbocharger compresses the air, but the high heat means that it’s difficult to maintain its density. A good intercooling system will improve the density and increase oxygen levels in the compressed mixture. This means that the combustion process will be made easier and with increased power, leading to a higher horsepower output.
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Exhaust flow
The flow of exhaust gases is critical to how both the engine and the turbocharger will perform. The turbocharger utilizes exhaust gases to propel power its function, and that’s why the interaction between the exhaust flow and the turbocharger is important.
The turbocharger’s work will not be your primary concern if there’s a problem with the exhaust flow system.
However, small leaks or restrictions can limit the turbo’s efficiency and overall engine performance. That’s how the exhaust flow is important in maintaining a functioning combustion process.
Types of Turbochargers
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Single-Turbos
Single turbochargers are what most people think of as turbos. By differing the size of the elements within the turbo, completely different torque characteristics can be achieved. Large turbos provide higher levels of top end power, whilst smaller turbos can spool faster and provide better low-end power. They are a cost-effective way of increasing engine power and efficiency, and as such have become increasingly popular, allowing smaller engines to increase efficiency by producing the same power as larger naturally-aspirated engines, but with a lower weight. They do however tend to work best within a narrow RPM range, and drivers will often experience ‘turbo-lag’ until the turbo starts to operate within its peak rev band.
Twin-Turbo
As the name implies twin-turbos mean adding a second turbocharger to an engine. In the case of V6 or V8 engines, this can be done by assigning a single turbo to work with each cylinder bank. Alternatively, one smaller turbo could be used at low RPMs with a larger turbo for higher RPMs. This second configuration (known as twin sequential turbocharging) allows for a wider operating RPM range, and provides better torque at low revs (reducing turbo lag), but also gives power at high RPMs. Unsurprisingly, having two turbos, significantly increases the complexity and associated costs.
Twin-Scroll Turbo
Twin-scroll turbochargers require a divided-inlet turbine housing and exhaust manifold that pairs the correct engine cylinders with each scroll. independently. For example, in a four-cylinder engine (with a firing order 1-3-4-2), cylinders 1 and 4 might feed to one scroll of the turbo, while cylinders 2 and 3 feed to a separate scroll. This layout provides more efficient delivery of exhaust gas energy to the turbo, and results and helps provide denser, purer air into each cylinder. More energy is sent to the exhaust turbine, meaning more power. Again, there is a cost penalty for addressing the complexity of a system requiring complicated turbine housings, exhaust manifolds and turbos.
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Variable Geometry Turbocharger (VGT)
Typically, VGTs include a ring of aerodynamically-shaped vanes in the turbine housing at the turbine inlet. In turbos for passenger cars and light commercial vehicles, these vanes rotate to vary the gas swirl angle and the cross-sectional area. These internal vanes alter the turbos area-to-radius (A/R) ratio to match the engines RPM, and so give peak performance. At low RPM, a low A/R ratio allows the turbo to quickly spool up by increasing exhaust gas velocity and. At higher revs the A/R ratio increases, ther4eby allowing increased airflow. This results in a low boost threshold reducing turbo lag, and provides a wide and smooth torque band.
Whilst VGTs are more typically used in diesel engines where exhaust gases are lower temperature, until now VGTs have been limited in petrol engine applications due to their cost and the requirement for components to be made from exotic materials. The high temperature of the exhaust gases means that the vanes must be made from exotic heat-resistant materials to prevent damage. This has restricted their use to applications within luxury, high performance engines.
Variable Twin-Scroll Turbocharger (VTS)
As the name suggests a VTS turbocharger combines the advantages of a twin-scroll turbo and a variable geometry turbo. It does this by the use of a valve which can redirect the exhaust airflow to just a single scroll, or by varying the amount the valve opens can allow for the exhaust gases to split to both scrolls. The VTS turbocharger design provides a cheaper and more robust alternative to VGT turbos, meaning it is a viable option for petrol engine applications
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Electric Turbochargers
An electric turbocharger is used to eliminate turbo lag and assist a normal turbocharger at lower engine speeds where a conventional turbo is not most efficient. This is achieved by adding an electric motor that spins up the turbo’s compressor from start and through the lower revs, until the power from the exhaust volume is high enough to work the turbocharger. This approach makes turbo lag a thing of the past, and significantly increases the RPM band within which the turbo will efficiently operate. So far, so good. It appears that electronic turbos are the answer to all the negative characteristics of conventional turbochargers, however there are some disadvantages. Most are around cost and complexity, as the electric motor must be accommodated and powered, plus also cooled to prevent reliability issues.
How to Choose the Right Turbo for Your HP Goals
Matching Turbo Size to Engine Capacity : Selecting the correct turbo size is crucial to achieving optimal HP gains without compromising engine performance or reliability.
Fuel Requirements for Turbocharged Engines : Higher octane fuel or specific blends (e.g., E85) are often recommended for turbocharged engines to optimize performance and prevent knock, a condition that can damage the engine at high boost levels.
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Turbocharger FAQ
What is the difference between a turbocharger and a supercharger?
How much horsepower does a turbocharger add?
Is a turbocharger bad for your engine?
What is the best turbocharger brand?
How much does a turbocharger cost?
