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On turbocharged engines, it’s been said, “If you want more power, you need to be willing to sacrifice some boost response.” Today, that’s actually seldom true. While you may be among the two-percent that have the best response turbocharger and turbo manifold for your engine combination, chances are that your current turbo and exhaust manifold do not feature all of the latest performance technologies. Ball-bearing center sections, bleeding-edge compressor and turbine wheel designs and surge-resistant compressor covers are just a few of the newer technologies that are allowing big-power turbos to have improved boost response. While exotic turbine materials, improved ball-bearing designs and new compressor make headlines, a twin scroll (a.k.a. divided-inlet) turbine housing paired with a properly-engineered turbo manifold may deliver a bigger improvement in boost response than a number of the other technologies combined. After reviewing the history and science behind twin scroll technology, we’ll show the real world differences of a single- versus twin scroll configuration on our Project KA turbocharged 240SX.
It’s only in the last 10 years that we’ve entered into our current era of “Modern Boost.” Now the supporting engine management technologies allow for a particular engine/turbocharger combination to be fully exploited. Both OEM and aftermarket engine management systems allow the fuel, boost and ignition curves to be optimized under a variety of load and throttle conditions. Boost response and power output can now be optimized to the limits of the particular engine/turbocharger combination. When selecting an upgraded turbocharger or complete new turbocharger system, the question of single- or twin-scroll must be answered.
Very well written article. Thank you for your contribution and time. Again! The 4g63 cam test you did was incredible.
Twin scroll is fun. One of the main reasons I still have a oem twin scroll on my car.
"Our test will change only one component, the turbine housing."
The test is flawed because they did not change the exhaust manifold and used the twinscroll merge collector with the open scroll turbine housing. The merge collector is actually part of the design of the twinscroll turbine housing. When you use the twinscroll merge collector on an open scroll turbine housing you are prematurely chocking down exhaust prior to reaching the open scroll housing.
I'm not saying that twinscoll is worse than open scroll in terms of response, but the test in the article is flawed.
"Our test will change only one component, the turbine housing."
The test is flawed because they did not change the exhaust manifold and used the twinscroll merge collector with the open scroll turbine housing. The merge collector is actually part of the design of the twinscroll turbine housing. When you use the twinscroll merge collector on an open scroll turbine housing you are prematurely chocking down exhaust prior to reaching the open scroll housing.
I'm not saying that twinscoll is worse than open scroll in terms of response, but the test in the article is flawed.
I'll agree that the test is not perfect, but I think the only difference in pairing a manifold designed for single scroll vs. using the twin-scroll manifold with the single scroll turbine housing will be peak power. I do not believe the transient response will be altered much. It might even be the case that using a single scroll manifold with the single scroll housing may negatively affect response.
I can see the benefit of using the twin-scroll manifold vs. single in that the twin-scroll still keeps the flows of the opposing cylinders separated until they are both flowing the same direction which is straight into the turbine housing. The negative would be the exhaust gas goes from the smaller (half) opening of the manifold into the large opening of the single scroll turbine housing which creates a flow loss.
Regardless, peak power numbers aside, this test clearly demonstrates the response advantage of a full twin-scroll setup which is why all the OEMs go through the trouble of implementing it. So I think the response question is clearly answered, and peak power is open for debate.
If that had a proper single scroll manifold, I think the results would be much different. The outlets of that t3 vband manifold are tiny, and definitely hurting power on the single scroll turbine housing, and may even be slowing spool a little bit. The test isn't valid. They could (should) have bought the same companies manifolds, one in SS and one in TS.
Especially when you consider an Evo, where single T3 cars usually use an exhaust housing n the .82 range for a 35r sized turbo, and when twin scroll is used, we step up to a t4 flange with AR somewhere in the 1.1-1.3 range depending on the turbo size.
Agreed, I think the best way you could do this test would be a thin-wall header with slip-fit collector. Swap the collector and the housing. Other then that, everything stays the same.
But...WHY?
If you are using TS correctly, you have chosen different cams, different compression ratio, different runner lengths....different everything. It's all about optimizing the system as a whole, not simply tossing some parts together and expecting the turbo to be the make or break difference in the end.
"Our test will change only one component, the turbine housing."
The test is flawed because they did not change the exhaust manifold and used the twinscroll merge collector with the open scroll turbine housing. The merge collector is actually part of the design of the twinscroll turbine housing. When you use the twinscroll merge collector on an open scroll turbine housing you are prematurely chocking down exhaust prior to reaching the open scroll housing.
I'm not saying that twinscoll is worse than open scroll in terms of response, but the test in the article is flawed.
Short Story:
The test IS NOT flawed in any way, shape or form. The test compared the difference in performance between a single- and twin-scroll turbocharger setup on a twin-scroll manifold.
The conclusion of the results is that if the performance combination is looking to maximize efficiency and performance, a twin-scroll will outperform a single-scroll setup.
Long Version:
For those forum pundits that believe we should have made a second manifold, that would have been a really bad idea. Here is why. In any test, the objective is to limit the possible sources of error. If we would have built a single-scroll manifold that positioned the turbo in the same location (allowing us to use the same exact charge piping configuration), the primary tube length of the header would have been shorter with the single-scroll. The difference in primary length would have been a possible source of error. In conducting the test as we did, the primary length was identical and we did not have any other sources of error from introducing a second manifold that may have had other differences.
So what about that divider choking off the flow? Are you ready for this? It doesn't in this case. As long as the cross-sectional area of a single-side of the twin-scroll manifold has a like cross-sectional area to the cross-sectional area of a single runner, no expansion or compression of the exhaust gasses occur (so no change in exhaust velocity). For the purpose of this test, the same expansion that would have occurred in the collector section of a single-scroll manifold instead occurs at the turbine inlet. In essence, it works as we did it. Of course, we could have spent weeks on optimizing an exhaust manifold for each turbine housing configuration. But it's our belief that we would have seen the exact same results.
I completely understand the basis behind the challenges posted. I believe it all boils down to how one looks at an engine. Conceptually, I also had a similar vision of how a performance engine works about 20 years ago. When engines are looked at as systems with constant flow rates in and out of the engine, this oversimplification can cause some problems. In actuality, the IC 4-stroke engine is moving flow in a series of pulses. These pulses sometimes overlap. The twin-scroll manifold allows the overlapping of exhaust cycles on cylinders to have less interference with each other.
I've had the fortune of having some great teachers when it comes to engine performance as its been my lifelong passion. After graduating from UCI with a degree in Mechanical and Aerospace Engineering, I jumped into the performance industry in 1994. As a technical editor at Turbo magazine back then, I had the opportunity to speak with Ken Duttweiler (the father of modern performance turbocharging). Engine building and tuning projects have been my life from Project Talon to my Project RH8 R33 GT-R. In 1998, I was blessed with being able to interact with racers from around the world when we launched the IDRC racing series. Allan Lockheed Jr. became a close friend shortly after when DRAG SPORT was launched. Allan has been developing engine programs for the past 50 years. Today, Magnus Ohlaker shares his F1, IndyCar and 20 years of Cosworth Engineering experience with me on a daily basis at our Club DSPORT engine development facility next store to our editorial office. I'm not putting out this information to brag and boast. I simply put it out there to let you know that the information in DSPORT is trustworthy. We are not reporters. We are the engineers, enthusiasts and engine builders that design, wrench and test in order to give our readers the right info.
I apologize that I'm having to waste peoples time to read this, but I understand that there is plenty of bad info out there and just wanted to let everyone know that the tests and info in DSPORT can be trusted. We truly appreciate the support of our readers. If you'd like to support us, please sign up for a subscription.
Short Story:
The test IS NOT flawed in any way, shape or form. The test compared the difference in performance between a single- and twin-scroll turbocharger setup on a twin-scroll manifold.
The conclusion of the results is that if the performance combination is looking to maximize efficiency and performance, a twin-scroll will outperform a single-scroll setup.
Long Version:
For those forum pundits that believe we should have made a second manifold, that would have been a really bad idea. Here is why. In any test, the objective is to limit the possible sources of error. If we would have built a single-scroll manifold that positioned the turbo in the same location (allowing us to use the same exact charge piping configuration), the primary tube length of the header would have been shorter with the single-scroll. The difference in primary length would have been a possible source of error. In conducting the test as we did, the primary length was identical and we did not have any other sources of error from introducing a second manifold that may have had other differences.
So what about that divider choking off the flow? Are you ready for this? It doesn't in this case. As long as the cross-sectional area of a single-side of the twin-scroll manifold has a like cross-sectional area to the cross-sectional area of a single runner, no expansion or compression of the exhaust gasses occur (so no change in exhaust velocity). For the purpose of this test, the same expansion that would have occurred in the collector section of a single-scroll manifold instead occurs at the turbine inlet. In essence, it works as we did it. Of course, we could have spent weeks on optimizing an exhaust manifold for each turbine housing configuration. But it's our belief that we would have seen the exact same results.
I completely understand the basis behind the challenges posted. I believe it all boils down to how one looks at an engine. Conceptually, I also had a similar vision of how a performance engine works about 20 years ago. When engines are looked at as systems with constant flow rates in and out of the engine, this oversimplification can cause some problems. In actuality, the IC 4-stroke engine is moving flow in a series of pulses. These pulses sometimes overlap. The twin-scroll manifold allows the overlapping of exhaust cycles on cylinders to have less interference with each other.
I've had the fortune of having some great teachers when it comes to engine performance as its been my lifelong passion. After graduating from UCI with a degree in Mechanical and Aerospace Engineering, I jumped into the performance industry in 1994. As a technical editor at Turbo magazine back then, I had the opportunity to speak with Ken Duttweiler (the father of modern performance turbocharging). Engine building and tuning projects have been my life from Project Talon to my Project RH8 R33 GT-R. In 1998, I was blessed with being able to interact with racers from around the world when we launched the IDRC racing series. Allan Lockheed Jr. became a close friend shortly after when DRAG SPORT was launched. Allan has been developing engine programs for the past 50 years. Today, Magnus Ohlaker shares his F1, IndyCar and 20 years of Cosworth Engineering experience with me on a daily basis at our Club DSPORT engine development facility next store to our editorial office. I'm not putting out this information to brag and boast. I simply put it out there to let you know that the information in DSPORT is trustworthy. We are not reporters. We are the engineers, enthusiasts and engine builders that design, wrench and test in order to give our readers the right info.
I apologize that I'm having to waste peoples time to read this, but I understand that there is plenty of bad info out there and just wanted to let everyone know that the tests and info in DSPORT can be trusted. We truly appreciate the support of our readers. If you'd like to support us, please sign up for a subscription.
Thank you for the reply and for providing a list of people you met over the years.
Regarding the primary tube length, I agree that fabricating a new manifold positioning the turbine housing in the same location would have changed the primary tube length. This difference would be the difference in the length of the cast vband merge collector, which is ~1.5". However, I think the effects on primary tube length would be negligible in comparison to sticking an open scroll housing onto a twinscroll merge collector. It is important to understand the cast vband merge collector is actually part of the turbine housing so where it vbands is within the scroll of the turbo. You can see what I mean from the pics below.
I understand the concept of staggering the exhaust pulses, but I do not agree with your statement that cross sectional area doesn't change. You are assuming the twinscroll begins at the vband, when it actually begins 1.5" upstream at the cast merge collector, which is actually part of the twinscroll turbine housing. Also, you assume the exhaust pulses are perfectly staggered and there is absolutely no overlap upon entering the merge collector, which is potentially a big assumption. If we assume the twinscroll begins at the vband and you used piping with an equivalent ID to 1.5" sched 40 weld els (1.625"), you can see how much larger the runner is overlay onto the opening of the vband twinscroll turbine housing in the first pic below. If we overlay the pipe on the cast vband merge collector it is actually smaller as you can see in the second pic below. Unless you ran a 2.0" ID primary you are going to have an increase in cross sectional area vs an individual runner at the entrance to the cast vband twinscroll flange.
The final point regarding change in cross section area is this, the outlets of the cast vband twinscroll flange have an approximate area of 1.5sq-in. When mounting an open scroll turbine housing onto the cast vband twinscroll flange you will merge all primaries into two 1.5sq-in openings (3.0sq-in) before they hit the open scroll, which has an ID of 2.1875" (3.76sq-in). So you are merging the exhaust within the cast vband twinscroll flange into the openscroll housing having an area that is ~22% larger. I think it is also safe to assume that a proper 4-1 merge collector designed for an open scroll turbine housing is going to flow better than the cast vband twinscroll flange designed for the twinscroll turbine housing.
Anyway, I agree that twinscroll is more responsive, but I believe there is potential for your openscroll results to be flawed.
Last edited by 240Z TwinTurbo; Mar 4, 2016 at 01:29 PM.
I was going to reference that exact build! lol. The exit of that collector is most definitely no where the cross sectional area of a manifold runner. That single scroll setup was being choked out. Likely effecting spool, and definitely effecting topend power. Especially when you consider the same AR was used between the TS and SS housing. And like I stated early, most guys will go from a T3 ss in .8-1.0 AR, and when going to TS, jump up to a T4 flange turbine housing in 1.1-1.4 AR.
Sorry, this test just didn't do it right. For a cam test, its fine to just change cams, adjust boost to equal, and do pulls. Hell, its even Ok to compare 3 different turbos in T3 single scroll, or 3 different turbos in twin scroll. But when comparing SS to TS, the manifold needs to be changed.
I was going to reference that exact build! lol. The exit of that collector is most definitely no where the cross sectional area of a manifold runner. That single scroll setup was being choked out. Likely effecting spool, and definitely effecting topend power. Especially when you consider the same AR was used between the TS and SS housing. And like I stated early, most guys will go from a T3 ss in .8-1.0 AR, and when going to TS, jump up to a T4 flange turbine housing in 1.1-1.4 AR.
The pictures are from my build.
FYI, with the new Garrett vband turbine housings, the 1.01 A/R twin scroll will have the same cross sectional area within the scroll as a 1.01 A/R open scroll. So from that perspective it is a good comparison.
letsgetthisdone: We respectfully disagree that the test was done incorrectly. We wouldn't have wasted our time, money and resources doing the test if it was going to produce flawed results.
240Ztwinturbo: Seriously, was your remark about downplaying the 20 years that I've dedicated to this industry necessary? You don't know me, I don't know you. I would never say something like, "Thank you for spending so much of your life on this forum to amass so many posts". Let's stop the downward spiral into personal attacks now. I'd imagine that you've helped a lot of people over the years, so why would I downplay that. Thank you for being an active member of this community.
Let's focus on the test.
We agree that fabricating two manifolds for the test would have resulted in different primary tube lengths. This along with other potential variances in the production of the manifold made using two manifolds a non-option.
There is no overlap in the exhaust pulses in each side of the exhaust manifold. This is not an assumption. It's a fact. The exhaust pulses are occurring 360 degrees apart from each other, so no overlap. During this period the exhaust valves from the paired cylinders have zero overlap.
I didn't say that the cross-sectional area was the same. I said that they were like or similar. Your calculated came up on the order of 20% for a distance of 1.5" before it reaches an open single scroll turbine housing. That's going to have a very negligible effect, if any.
Any test can be done a different way. I stand by the our testing method and procedure and would not change it based on any of the arguments offered thus far. In fact, if someone can prove that the conclusions of the test are flawed, I'll be more than happy to pay them $1,000 and buy them a beer.
The conclusion of the results is that if the performance combination is looking to maximize efficiency and performance, a twin-scroll will outperform a single-scroll setup.
Just a quick question...do people commenting have the actual article in print or are they looking at just the online version? I believe the print version is better as it contains more images and diagrams.
letsgetthisdone: We respectfully disagree that the test was done incorrectly. We wouldn't have wasted our time, money and resources doing the test if it was going to produce flawed results.
240Ztwinturbo: Seriously, was your remark about downplaying the 20 years that I've dedicated to this industry necessary? You don't know me, I don't know you. I would never say something like, "Thank you for spending so much of your life on this forum to amass so many posts". Let's stop the downward spiral into personal attacks now. I'd imagine that you've helped a lot of people over the years, so why would I downplay that. Thank you for being an active member of this community.
Let's focus on the test.
We agree that fabricating two manifolds for the test would have resulted in different primary tube lengths. This along with other potential variances in the production of the manifold made using two manifolds a non-option.
There is no overlap in the exhaust pulses in each side of the exhaust manifold. This is not an assumption. It's a fact. The exhaust pulses are occurring 360 degrees apart from each other, so no overlap. During this period the exhaust valves from the paired cylinders have zero overlap.
I didn't say that the cross-sectional area was the same. I said that they were like or similar. Your calculated came up on the order of 20% for a distance of 1.5" before it reaches an open single scroll turbine housing. That's going to have a very negligible effect, if any.
Any test can be done a different way. I stand by the our testing method and procedure and would not change it based on any of the arguments offered thus far. In fact, if someone can prove that the conclusions of the test are flawed, I'll be more than happy to pay them $1,000 and buy them a beer.
The conclusion of the results is that if the performance combination is looking to maximize efficiency and performance, a twin-scroll will outperform a single-scroll setup.
That's like saying the expansion valve/orifice tube in an automotive HVAC system has no effect on flow because the orifice is only 1/2" long.
The flow of a system (turbo and manifold for example) is only as good as it's most restricted point. a 20% reduction in cross sectional area is HUGE.
Mar 2, 2016, 01:17 PM
