Divided vs Undivided Turbine Housing

We recently released a Power Driven S480 turbo. When we were designing this turbo, we had to decide if we were going to use a divided housing or a new undivided housing. We chose an undivided housing for this turbo. Read on to find out why we chose an undivided housing, how these turbo housings compare to each other, and determine which is best for your application.

What is a divided or undivided turbo housing?

In a divided turbo housing, essentially the turbo scroll has been split into two smaller housings that run side-by-side in the scroll. This is sometimes called a twin-scroll housing. This separation allows the exhaust from the back three cylinders to flow through one port and the exhaust from the front three cylinders to flow through the other. The goal of this is to isolate the pulse from each cylinder into its own chamber, leading to awesome spool up at low RPM performance. It was designed for, and works very well for over-the-road semi applications.

The downside to divided housings is that once you get up to higher RPMs and higher RPM applications, the pulses can start backing up and you will end up with drive pressure issues. As a result, for high power applications, we have found that these absorb a lot of heat and can have the divider melt out.

A non-divided or undivided housing will have a single port through the scroll. These are sometimes called single scroll housings. We prefer these for high power applications, especially if you are pushing 1,000hp or more. With an undivided housing, you can really drop the drive pressure as the exhaust gasses are not backing up in the small twin-scrolls.

Since the undivided housing does not have the divider in the scroll absorbing heat, that heat is able to go to the turbine wheel to help you make more power.

The Power Driven S480 Turbo Features

We often see divided housing turbos used as the downstream turbo in a compound system. While this application does not see as much choking at high RPMs as divided turbines connected exactly to the exhaust manifold, it is still an inefficient use because it doesn’t take advantage of the design of the turbine housing and the divider still absorbs heat energy that would otherwise be used to make power.

This is why we designed the Power Driven S480 undivided housing. We wanted the benefits of a 400 series turbo, but also the benefits of the undivided housing – and we could not find that. We also incorporated a 4-inch pipe that was easier for most people to work with, accomplishing our goal of a turbo that was easy to fabricate and fit under the hood of your truck.

Divided Vs Non-Divided Turbine Housing Dyno Test

Next we wanted to test which turbine housing is superior and have some empirical data to back up the claim tha the undivided housing is better. We used the Junker Drag Truck to dyno test these two turbos. We know the undivided turbo is better when mounted directly to your manifold, so in these tests, we wanted to see how the divided vs undivided housings compare as the atmosphere turbo in a compound system.

In the results below, the dotted line is the Power Driven undivided housing with a 4” outlet. The other two dashed lines represent divided housings we tested.

First you will see that the runs are very consistent because of the precise fuel control the Junker provides. Across the board, you will note that the Power Driven housing is consistently about 4hp above the divided housings. We attribute this to the housing being unrestricted in its exhaust flow.

We also see the fastest boost rise is the 1.15 divided housing. This coincides with the drive pressure of the 1.15 housing also being the highest.

These are all really similar in performance until the boost really starts coming in and thats when we start to see the diversion between these different housings. At this point, we see that the 1.32 housing is really the slowest and lowest performing housing in these tests.

At 3,100 plus RPMs, we see the separation even more. The two divided housings start to come together and perform about the same, while the non-divided housing stays much higher and more efficient, as much as 27 more horsepower.

When we look at the time of the runs, we really start to see how differently these turbo housings perform. For example, these all start out very similar, but by the time we are 3 seconds into the run, the non-divided housing is making nearly 50hp more than the 1.32 housing, and nearly 60hp more than the 1.15 housing. Its not until about 5.5 seconds that the other housings catch up, but they quickly fall off through top end RPMs.

You will also notice that the non-divided housing is also making less interstage boost, but is making more power. It appears to be a much more efficient housing.

Finally, we put a tow tune in the truck to see how this setup tows. A lot of people use this setup for towing, and it does well in this application. You will notice in the tow test that these all performed well, but the undivided housing is the winner across the entire tow.

Note that if you are doing a lot of towing, a compound setup will keep your EGTs lower and improve performance of your engine. We really recommend a compound setup if you are doing a lot of towing with your truck.

In conclusion, we feel that an undivided housing is the way to go in a compound setup. But let us know what you think or what questions you have. Leave a comment below or head over to our Facebook and Instagram pages.

Contact us with any questions you have about parts and products for your truck. Our team is here to help. Give us a call at 435-962-9555 or text us at 435-962-9506 or leave us a comment below. Don’t forget to follow us on YouTube, Facebook, and Instagram for more product tests. Leave us a comment below about what you’d like us to cover next.