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      02-13-2014, 06:22 PM   #1
curehead
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S55 mono-scroll turbo vs. N55 twin-scroll turbo

I tried already searching for an explanation, but can't find any more details on how these actually work and what the difference is.
I understand the new S55 engine has two mono scroll Mitsubishi turbos while the N55 has a single twin scroll turbo. But how do the two turbos in the new one work? Do they run simultaneously or subsequently?

Thanks!
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      02-13-2014, 06:37 PM   #2
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Twin scroll refers to the exhaust channeling before it reaches the turbo. Exhaust is produced in phases based on the firing order on the engine. In a twin scroll turbo, the exhaust manifold is routed in such a way to optimize exhaust flow from the engine so that the turbo is receiving an optimal amount of exhaust flow (I.e. optimal would have the turbo receiving exhaust flow 100% of the time instead of in phases).
The S55 will function in the same manner the n54 did. Two exhaust manifolds that connect to two turbos. So expect to see something to the effect of turbo one fed by cylinder 1-3 and turbo two by cylinders 4-6.
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      02-13-2014, 06:38 PM   #3
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Quote:
Originally Posted by jlh335i View Post
Twin scroll refers to the exhaust channeling before it reaches the turbo. Exhaust is produced in phases based on the firing order on the engine. In a twin scroll turbo, the exhaust manifold is routed in such a way to optimize exhaust flow from the engine so that the turbo is receiving an optimal amount of exhaust flow (I.e. optimal would have the turbo receiving exhaust flow 100% of the time instead of in phases).
The S55 will function in the same manner the n54 did. Two exhaust manifolds that connect to two turbos. So expect to see something to the effect of turbo one fed by cylinder 1-3 and turbo two by cylinders 4-6.
Typically also means smaller turbos can be used and less turbo lag
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      02-13-2014, 11:55 PM   #4
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Quote:
Originally Posted by curehead View Post
I tried already searching for an explanation, but can't find any more details on how these actually work and what the difference is.
I understand the new S55 engine has two mono scroll Mitsubishi turbos while the N55 has a single twin scroll turbo. But how do the two turbos in the new one work? Do they run simultaneously or subsequently?

Thanks!
The S55 will have a twin turbo system similar to the N54: 1 monoscroll turbo per 3 cylinders.

The N55 has a single turbo with twinscroll technology: 1 turbo with 2 channels for 6 cylinders.

Mono scroll has a single channel within its turbine housing. Twinscroll has 2 channels of different volumes within its turbine housing (not to be confused with divided turbine housing with 2 channels of the same volume). Having 2 channels within its turbine housing enables cylinders to pulse exhaust gases evenly onto the turbine blade to improve spool. Twinscroll technology enables quick spool per 1 channel, with optimal flow in the other channel (divided housing has channels of the same size, so both are for optimal flow). However, monoscroll turbine housings outflow twinscroll and divided housings. Below are pictures to help visualize what I'm trying to convey:

Monoscroll (basic):


Twinscroll (note the 2 channels have different volumes, 1 for velocity/spool, 1 for flow):


Divided housing (note the 2 channels have the same volume, both for flow):


To answer your question, no one really knows unless the tech specs are released. I can't imagine BMW M to NOT use N54 style setup (both actuated simultaneously) rather than a bi-turbo setup circa mk4 supras (1 small turbo and 1 large turbo where the smaller helps with spool and the larger helps with flow) since the N54 and Alpinas have proven to work just fine.

TLDR;
monoscroll = 1 channel in turbine housing
twinscroll = 2 channels in turbine housing, different sizes
divided housing = 2 channels in turbine housing, same size
S55 = Simultaneous, according to N54 and Alpinas? TBA
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      02-14-2014, 02:57 AM   #5
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Quote:
Originally Posted by Andy0323 View Post
The S55 will have a twin turbo system similar to the N54: 1 monoscroll turbo per 3 cylinders.

The N55 has a single turbo with twinscroll technology: 1 turbo with 2 channels for 6 cylinders.

Mono scroll has a single channel within its turbine housing. Twinscroll has 2 channels of different volumes within its turbine housing (not to be confused with divided turbine housing with 2 channels of the same volume). Having 2 channels within its turbine housing enables cylinders to pulse exhaust gases evenly onto the turbine blade to improve spool. Twinscroll technology enables quick spool per 1 channel, with optimal flow in the other channel (divided housing has channels of the same size, so both are for optimal flow). However, monoscroll turbine housings outflow twinscroll and divided housings. Below are pictures to help visualize what I'm trying to convey:

Monoscroll (basic):


Twinscroll (note the 2 channels have different volumes, 1 for velocity/spool, 1 for flow):


Divided housing (note the 2 channels have the same volume, both for flow):


To answer your question, no one really knows unless the tech specs are released. I can't imagine BMW M to NOT use N54 style setup (both actuated simultaneously) rather than a bi-turbo setup circa mk4 supras (1 small turbo and 1 large turbo where the smaller helps with spool and the larger helps with flow) since the N54 and Alpinas have proven to work just fine.

TLDR;
monoscroll = 1 channel in turbine housing
twinscroll = 2 channels in turbine housing, different sizes
divided housing = 2 channels in turbine housing, same size
S55 = Simultaneous, according to N54 and Alpinas? TBA
Thanks for your answer!
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      02-14-2014, 04:08 AM   #6
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Quote:
Originally Posted by Andy0323 View Post
To answer your question, no one really knows unless the tech specs are released. I can't imagine BMW M to NOT use N54 style setup (both actuated simultaneously) rather than a bi-turbo setup circa mk4 supras (1 small turbo and 1 large turbo where the smaller helps with spool and the larger helps with flow) since the N54 and Alpinas have proven to work just fine.

TLDR;
monoscroll = 1 channel in turbine housing
twinscroll = 2 channels in turbine housing, different sizes
divided housing = 2 channels in turbine housing, same size
S55 = Simultaneous, according to N54 and Alpinas? TBA
Looking at the pictures of the engine in the official threads, it's evident that the S55 uses two similar turbos in parallel. So that question has been answered quite some time ago

http://f80.bimmerpost.com/forums/sho...d.php?t=923444

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      02-14-2014, 04:11 AM   #7
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Quote:
Originally Posted by jlh335i View Post
Twin scroll refers to the exhaust channeling before it reaches the turbo. Exhaust is produced in phases based on the firing order on the engine. In a twin scroll turbo, the exhaust manifold is routed in such a way to optimize exhaust flow from the engine so that the turbo is receiving an optimal amount of exhaust flow (I.e. optimal would have the turbo receiving exhaust flow 100% of the time instead of in phases).
The S55 will function in the same manner the n54 did. Two exhaust manifolds that connect to two turbos. So expect to see something to the effect of turbo one fed by cylinder 1-3 and turbo two by cylinders 4-6.
Twin scroll is exhaust channeling inside the turbo, not before the turbo. You are possibly thinking of impulse charging?

And, we have allready photos of the exhaust manifolds that shows the 1-3 and 4-6 routing you mention

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      02-14-2014, 09:39 AM   #8
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^ I was refering to the orientation of the exhaust manifold that easily distinguishes any twin scroll setup from a traditional turbo. A twin scroll turbo system begins with a manifold that routes exhaust gases according to the firing order of the engine.
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      02-14-2014, 12:01 PM   #9
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Quote:
Originally Posted by jlh335i View Post
^ I was refering to the orientation of the exhaust manifold that easily distinguishes any twin scroll setup from a traditional turbo. A twin scroll turbo system begins with a manifold that routes exhaust gases according to the firing order of the engine.
Twin scroll refers to the design of the turbine housing with two exhaust channels in the turbine housing itself.

On a I6, the routing of the exhaust manifold is similar both on the N55 single turbo twin scroll and the S55 twin turbo mono scroll setup. On a I6 you want to route the exhaust from cyl 1-3 and 4-6 into either each turbo (as per N54/S55) or to each of the scrolls in a twin scroll turbo (as per N55). On a N55 exhaust manifold, it's not really outwardly visible that there is a twin scroll turbo. It looks like a common I6 exhaust manifold leading to one turbo, but with cyl 1-3 separated from cyl 4-6 internally at the mounting flange to the turbo.











However on the I4 N20, you want cyl 1-4 and 2-3 routed together:



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      02-14-2014, 03:18 PM   #10
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You over complicate things too much. Before the divided turbo housing was put to use, twin scroll manifolds were used to optimize exhaust flow to turbos. Colloquial in the tuning world.

https://www.google.com/webhp?tab=ww&...croll+manifold
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      02-14-2014, 03:52 PM   #11
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Quote:
Originally Posted by jlh335i View Post
You over complicate things too much. Before the divided turbo housing was put to use, twin scroll manifolds were used to optimize exhaust flow to turbos. Colloquial in the tuning world.

https://www.google.com/webhp?tab=ww&...croll+manifold
Over complicate?

I just pointed out basically the same you said about a twin scroll turbo and exhaust manifold, but also pointed out that the N55 manifold doesn't really advertice that it feeds a twin scroll turbo.

However, a twin exit exhaust manifold (or a twin scroll manifold) wouldn't really bring any advantage on a single scroll turbo. So, IMHO the concept of a twin scroll manifold makes little sense without a twin scroll turbo...

From one of the pages in your link:

http://www.forcedinductionsonline.co...roduct_id=1136

Quote:
Full-Race's legendary twin-scroll turbo manifold is now available for the Mitsubishi 4B11T Evolution X. The Big Runner's 40mm runner diameter is intended for our drag race applications which typically have ported cylinder head, high flowing valve job, largely oversized cams and plan to run 30+ psi of boost.

This header is designed to be versatile and fit a variety of different style twin-scroll T4 turbochargers from many manufacturers - Borg Warner, Garrett, HKS, Precision, FP, etc will all fit. The twin-scroll turbo manifold design spools large turbos fast for torque gains and faster transient response than traditional undivided single-scroll turbos. Single-scroll T4 will also fit, but loses low end torque/midrange and transient response.

So, as you can see. The manifold design doesn't really bring any major advantages if not coupled with a twin scroll turbo. It's the turbo, with it's dual exhaust channels that gives the name to "Twin Scroll". The manifold is "just" a means of optimizing exhaust flow to the twin scrolls in the turbo.

Notice that the "twin scroll" part is referring to the turbo design (turbine housing):



http://en.wikipedia.org/wiki/Turbocharger


Twin Scroll refers to turbo design and not to a exhaust manifold design. A "twin scroll manifold" is just a manifold that is made for a twin scroll turbo. The name "twin scroll" comes from the turbo, not the manifold


Difference (and similarity) between a twin scroll style manifold and a single scroll style manifold:



A single twin scroll turbo I6 manifold:



As you can see, it's not THAT easy to tell them apart when they are on the engine with a turbo attached...

Good info on turbo and manifold design:

http://forum.ih8mud.com/80-series-te...-faq-info.html

Quote:
A design feature that can be common to both manifold types is a " DIVIDED MANIFOLD" , typically employed with " DIVIDED " or "twin-scroll" turbine housings. Divided exhaust manifolds can be incorporated into either a cast or welded tubular manifolds (see Figure 5. and Figure 6.).

The concept is to DIVIDE or separate the cylinders whose cycles interfere with one another to best utilize the engine's exhaust pulse energy.

For example, on a four-cylinder engine with firing order 1-3-4-2, cylinder #1 is ending its expansion stroke and opening its exhaust valve while cylinder #2 still has its exhaust valve open (cylinder #2 is in its overlap period). In an undivided exhaust manifold, this pressure pulse from cylinder #1's exhaust blowdown event is much more likely to contaminate cylinder #2 with high pressure exhaust gas. Not only does this hurt cylinder #2's ability to breathe properly, but this pulse energy would have been better utilized in the turbine.

The proper grouping for this engine is to keep complementary cylinders grouped together-- #1 and #4 are complementary; as are cylinders #2 and #3.

Because of the better utilization of the exhaust pulse energy, the turbine's performance is improved and boost increases more quickly.

Last edited by Boss330; 02-14-2014 at 04:03 PM..
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      02-14-2014, 06:40 PM   #12
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      09-18-2014, 10:37 PM   #13
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Quote:
Originally Posted by curehead View Post
I understand the new S55 engine has two mono scroll Mitsubishi turbos while the N55 has a single twin scroll turbo.

Thanks!
I believe they are using Honeywell Turbos (previously known as Garett)
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      10-21-2014, 04:10 PM   #14
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Can anyone tell me if BMW website is right or wrong. On the site it says that the the Z4 35i and z4 35is have 2 Twin scroll turbos. But every dealer I have called says it has single scroll. I have called may dealers and Dinan and no one seems to know the answer.


Here is the link to the specs page on the BMW site: http://www.bmwusa.com/Standard/Conte...and_Specs.aspx

I am trying to buy some parts for my car and I cant seem to find anything for 2014 up. All the parts listed only go to 2013. When I call the places they all say yes it will fit but when I mention that it has 2 twin scroll turbos they say they don't know because they have not worked on any new Z4.
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