In the automobile industry, we refer to twin scroll turbos as revolutionary inventions in the forced induction world. But what is a twin scroll turbo, and what kind of benefits does this application offer?
As a type of turbocharger, the twin scroll turbo has a lot to offer. In our guide, we will explain everything you need to know about twin scroll turbos by looking at the working principles and comparing them to similar setups.
Source: shutterstock.com / Photo Contributor: vershandrey
What Is a Twin Scroll Turbo?
Before we explain the twin scroll turbo meaning, we should give you a little bit of perspective. Turbochargers have two main challenges – reducing turbo lag and ensuring exhaust flow.
Since the invention of turbochargers, engineers have been struggling to find the ultimate solution to these two problems. Thus, several types of turbochargers have been designed.
One of the efficient ways to deal with turbo lag and exhaust flow is the twin scroll turbocharger. But what does twin scroll turbo mean, and how is it different from other turbocharger settings?
Similarly to some of its counterparts, the twin scroll turbo has single turbo housing and a single turbine blade. However, how it is different from them is that it features two channels, which are also called “scrolls”.
Twin scroll turbos have an exhaust manifold, which is divided into two scrolls. Each one of them is individually connected to the engine cylinders and gets half of the engine’s exhaust.
Such a layout handles the delivery of the exhaust gas energy to the turbo more efficiently. As a result, the air in the cylinders is purer and denser, which positively affects the engine performance.
How Does a Twin Scroll Turbo Work?
Twin scroll turbos are categorized as pulse-turbocharged systems that use both thermal and pulse energy. That means that the twin scroll turbocharging setups capture the exhaust pulses from different pairs of engine cylinders.
The twin scroll turbocharger is capable of producing a higher turbine inlet energy due to the exploitation of pressure waves. The exhaust streams from the cylinder pairs are routed to the turbine. They pass the spiral-shaped channels, which have different diameters. The spiral-shaped channels, or scrolls, direct the exhaust stream to the turbine blades.
Typically, the larger channel is connected to the middle cylinders. It navigates the exhaust stream to the outer edge of the turbine blades. Because of this, the turbocharger spins faster.
On the contrary, the smaller scroll is connected to the end cylinders. If the bigger scroll directs the exhaust stream to the outer space of the turbine blades, the smaller scroll directs them to the inner surface. Thanks to the smaller scroll, the response of the turbocharger during acceleration should be improved.
Pros and Cons of Twin Scroll Turbos
Our guide on twin scroll turbo wouldn’t be complete without the advantages and disadvantages of the turbocharged engine.
The twin scroll turbo engines offer numerous benefits, which include, but are not limited to:
- Increase in low-end torque
- Reliability
- Improve boost response
- Up to 8% more efficiency throughout the rev range
- Power rises throughout the powerband
- Maximized turbine efficiency
- Less engine pumping losses
- Better fuel consumption up to 5%
- Lower exhaust gas temperatures
- Decreased intake charge dilution during valve overlap
The list of limitations of twin scroll turbos is shorter. Firstly, they aren’t proven to be efficient at high engine load and speed. Secondly, the exhaust manifold and turbine casing are generally complex and expensive.
Applications of Twin Scroll Turbos
Twin scroll turbos, their unique design, and working principle prevent them from being applicable to any engine. For instance, although it is not impossible to apply them, twin scroll turbos are not generally used on engines with three or five cylinders.
The common application of twin scroll turbos is high-end gasoline engines. This is especially the case for vehicles with high engine torque at lower speeds.
We recommend using the twin scroll technology on combustion engines with pulse overlap. At best, the twin scroll systems are suitable for engine displacement ranges between 1.5 and 2.5 liters.
Twin scroll turbos have been a turbocharger of choice for many brand vehicles such as Toyota, Mitsubishi, Pontiac Solstice, JDM Impreza, and many more.
What Is the Difference Between Mono and Twin Scroll Turbos?
Single turbos are also known as mono turbos and constant-pressure turbochargers. They are fueled by one shared pipe. This one scroll directs the exhaust gas from all the cylinders towards the turbine. The turbine housing has a single volute that transforms the exhaust energy into compressor rotation.
The first difference between single scroll and twin scroll turbos is the ease of installation. Because of their simpler design, single scroll turbos are easier to install. They are also more compact than twin scroll turbos.
Next, compared to twin scrolls, single scroll systems have more trouble handling the various pulses as they collide with each other. Consequently, single turbos might cause turbo lag and reduce the efficiency of the engine.
When it comes to RPM performance, single turbos are better for high RPM performance, while twin scroll turbochargers produce better low RPM performance. So, single scroll turbos are better if you opt for a higher boost, while twin scroll turbos are preferred for daily city rides.
Horsepower comparison between twin-scroll and single-scroll
|
RPM |
Twin-scroll |
Single-scroll |
Change in HP |
Percentage change |
|
3,000 |
65.09 |
62.11 |
2.98 |
4.8% |
|
4,000 |
162.66 |
136.89 |
25.77 |
16.28% |
|
5,000 |
360.12 |
298.38 |
61.74 |
20.69% |
|
6,000 |
550.56 |
529.04 |
21.52 |
4.07% |
|
7,000 |
611.90 |
610.86 |
1.04 |
0.17% |
What Is the Difference Between Twin Scroll Turbo and Variable Twin Scroll Turbo?
In our years of experience, we have seen many people confusing the twin scroll turbos with variable twin scroll turbo setups. But, there is a difference in the way they work.
The variable twin scroll turbo is a combination of two types of turbochargers – the variable geometry and twin scroll turbo. In other words, the variable twin scroll turbo uses the benefits of the two setups.
What makes the variable twin scroll turbo different from its parent, the twin scroll, is the valve. The valve moves so it can force the gasses to go into different scrolls. How the variable twin scroll turbos work is:
- In a low A/R ratio, the valve forces the gasses into one scroll allowing the vehicle to go into boost quickly.
- As you increase the RPMs, the valve will open slightly, letting some of the exhaust in the second scroll.
- Finally, in a high A/R ratio, the valve will open up so it can equally distribute the gasses between the two scrolls.
Source: shutterstock.com / Photo Contributor: Philip Lange
Frequently Asked Questions
Do twin scroll turbos spool faster?
Yes, the two scroll system splits the exhaust flow into two separate paths using a divided turbine housing. This allows for more efficient and faster spooling of the turbocharger. The gasses typically move faster in such narrow chambers.
Are twin scroll turbos better than single turbos?
When you compare the twin scroll turbos and single turbos both have their pros and cons. Twin scroll turbos are more efficient and produce less turbo lag, while single scroll turbos are easier to install.
Are twin scroll turbos worth it?
Whether twin scroll turbos are worth it depends on your preferences. If you want to benefit from improved and quicker boost response, maximized turbine efficiency, and reduced fuel consumption, twin scroll turbos might be worth it.
Can you install a twin scroll turbos on every engine?
Theoretically looking, twin scroll turbos can be installed on every engine. But, in reality, they work best on engines with an even number of cylinders. Also, it is quite a challenge to install a twin scroll turbo on engines with cylinders on demand.
Conclusion
To use its full potential, you must understand what is a twin scroll turbo. It stands as an innovative solution in the modern automotive technology. Among the other benefits, it enhances engine performance by optimizing the exhaust gas flow with the separated inlet channels.
We predict that twin-scroll turbos will continue to improve the performance of many vehicles. If you want to install one on your car, you can check our inventory and browse through the new and rebuilt models.
