Small article on Autoweek

[cj428]

http://www.autoweek.com/article/car-news/2015-ford-mustang-technical-overload

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[SLVRBACK]

Lost credibility with me at " mimicking a twin-turbocharger "

 

[EXP Jawa]

They got the axle info wrong as well. They got a hold of the correct thread, but didn't comprehend what Ford actually did.

 

[buRNout]

They got the axle info wrong as well. They got a hold of the correct thread, but didn't comprehend what Ford actually did.

Yeah I saw that also. Made me think of Clarkson on Top Gear; Did a hair dresser write this? :shrug:

 

[Feeshta]

Lost credibility with me at " mimicking a twin-turbocharger "

A twin scroll actually does basically exactly that. It eliminates the need to use a twin turbo system by separating the exhaust pulses into seperate paths through the turbo. This allows them to space out the incoming pulses in such a way that they avoid the negative pressure from the previous cylinder's down-stroke, instead waiting until after it has past, thus improving actual boost levels.

Twin turbo systems existed for two seperate reasons generally. To achieve this separation and better performance, or purely for packaging reasons. The two turbos were typically roughly half the output that a single turbo would be in the same application. In other words, it wasn't about more overall boost, it was about less lag and better efficiency. There were some other fringe applications like a sequential turbo system, but they are rare.

 

[SLVRBACK]

A twin scroll actually does basically exactly that. It eliminates the need to use a twin turbo system by separating the exhaust pulses into seperate paths through the turbo. This allows them to space out the incoming pulses in such a way that they avoid the negative pressure from the previous cylinder's down-stroke, instead waiting until after it has past, thus improving actual boost levels.

Twin turbo systems existed for two seperate reasons generally. To achieve this separation and better performance, or purely for packaging reasons. The two turbos were typically roughly half the output that a single turbo would be in the same application. In other words, it wasn't about more overall boost, it was about less lag and better efficiency. There were some other fringe applications like a sequential turbo system, but they are rare.

A twin scroll turbo simply utilizes a seperation of exhaust pulses to make it the most efficient and smooth as possible. I personally dont think it mimics a twin-turbo system at all, bi-turbo maybe because the whole idea is to reduce lag.

 

[Trevon]

...twin turbo is just a name for having two turbos...

In the diesel world "twins" can mean a 66mm over an S480 or whatever, it doesn't mean you have two of the same turbo...

 

[SLVRBACK]

...twin turbo is just a name for having two turbos...

In the diesel world "twins" can mean a 66mm over an S480 or whatever, it doesn't mean you have two of the same turbo...

Twin turbo means two of the same turbo, hence twin.

Bi-turbo is having two different size turbos. one for low end and one for high end.

Kind of like how wheel and rim are not the same thing but people think they are.

 

[Feeshta]

A twin scroll turbo simply utilizes a seperation of exhaust pulses to make it the most efficient and smooth as possible. I personally dont think it mimics a twin-turbo system at all, bi-turbo maybe because the whole idea is to reduce lag.

The reason twin turbo systems were typically used is for exactly that pulse separation, which reduces lag and increases efficiency. The thing is, nobody in their right mind will actually use two turbos anymore when a single twin scroll can achieve the same result. The only reason not to use a twin scroll is if packaging prohibits it, such as in some cases where the plumbing just wouldn't be feasible.

Twin scrolls are more thermally efficient than going the twin turbo route, are less costly, more reliable, easier to maintain, and have less lag.. This is why BMW went from the twin turbo N54 to the Twin scroll N55. The only reason not to use one is cost cutting or extreme boost applications.

Bottom line, they are correct that is mimics the effect of a twin turbo system, but it's better than just that. It's simply a superior format.

 

[Feeshta]

Twin turbo means two of the same turbo, hence twin.

Bi-turbo is having two different size turbos. one for low end and one for high end.

Kind of like how wheel and rim are not the same thing but people think they are.

Twin turbo and bi-turbo are mostly marketing terms. There are other more technically correct names for the formats you just mentioned, as there are several different types of twin turbo systems that serve different purposes and function in different ways, and several different types of so called Bi-turbo systems as well. You can have a twin turbo system that does not take advantage of pulse separation, like in the case of a V8 engine with a turbo per side and no connection between them. It's slightly different than just being a 4 cylinder with a single scroll turbo, as a V8 typically uses a cross-plane crank vs an inline 4's flat-plane, and the firing orders the turbo would see are a bit different. The end result is pretty similar though, as the pulses would not be ideally aligned to maximize efficiency.

This makes me wonder about something. I heard a rumor a while ago that Ford was planning a 650HP flat-plane twin turbo V8 for a future Shelby. I wonder if they are planning to use dual twin scroll turbos, essentially putting two of the 2.3 Ecoboost engines together at the crank? That could make for a really interesting power plant. Twin scrolls are ideally suited to the flat plane 4 cylinder configuration and the power number is basically 2 times the EB engine, so it makes a lot of sense.

 

[Trevon]

Bi-turbo isn't for low and high unless there's a bypass which is extremely unlikely and very complicated. Your definition of "bi-turbo" would be for quick spooling. The small turbo feeds the big turbo. Everything is "twins." The term "bi-turbo" came from OEM naming. If you wanted a real difference it would be twin and compound...but everything is twins.

 

[Trackaholic]

Bi-turbo isn't for low and high unless there's a bypass which is extremely unlikely and very complicated. Your definition of "bi-turbo" would be for quick spooling. The small turbo feeds the big turbo. Everything is "twins." The term "bi-turbo" came from OEM naming. If you wanted a real difference it would be twin and compound...but everything is twins.

I've also heard the term "sequential" used to refer to the case where a small turbo spools first and then switches over to a larger turbo at higher RPMs. I think the last generation RX-7 used this method.

-T

 

[Stroked84]

Yeah, the FD RX7 and MkIV Supra's both used sequential twin turbos, whereas the 300ZX and 3000GT's used parallel twin turbos. Which made sense when you look in the engine bay. 300ZX/3000GT = V6's, exhauste on both sides of the block. RX7/Supra Rotary and I6, exhaust ports all on one side. It made logical sense, IMO anyway.

"The twin turbos operated in sequential mode, not parallel. Initially, all of the exhaust is routed to the first turbine for reduced lag. This resulted in boost and enhanced torque as early as 1800 rpm, where it already produced 300 lb·ft (410 N·m) of torque. At 3500 rpm, some of the exhaust is routed to the second turbine for a "pre-boost" mode, although none of the compressor output is used by the engine at this point. At 4000 rpm, the second turbo's output is used to augment the first turbo's output. Compared to the parallel mode, sequential mode turbos provide quicker low RPM response and increased high RPM boost."

 

[JimmyTwoTimes]

There's also that twin-charging thing VW tried for a while with supercharging for low-rpm boost and turbos on the high end.

 

[DivineStrike]

They had a few people in the mk 1 Focus community twin charge their rides.

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