02-13-2014, 06:22 PM | #1 |
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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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02-13-2014, 11:55 PM | #4 | |
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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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02-14-2014, 04:08 AM | #6 | |
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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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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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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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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:
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:
Last edited by Boss330; 02-14-2014 at 04:03 PM.. |
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09-18-2014, 10:37 PM | #13 |
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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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