Twin Turbos

[rayyan171]

279 said:

rayyan171 said:

It definitely is a cheaper and better alternative to adding 2 turbos instead as it puts less pressure on the block and produces less emissions, boost is at the highest and most efficient pressure so that helps too. It also saves on fuel as well.

Other manufacturers find it difficult to adapt because of the significant change in internals when changing from twin turbo to twin scroll. But, ford is using it and lexus too, so I am guessing other manufacturers will eventually catch on.

Could you please elborate a little more on the "significant change in internals" required for a twin scroll setup, and why they are required? I was under the impression that it is all in manifold and turbo design?

I can think of a few aftermarket applications where twin scroll turbos have been retrofitted to cars that used traditional turbos, through the use of specifically designed manifolds, seemingly with no issues.

Edited by 279 on Wednesday 7th December 02:30

Cars that use traditional single turbos can take twin scroll turbos with modified manifolds, as you have stated.
However, in the case of BMW, they did actually rethink the engine and ended up creating a new engine with new engine code (N55) when they made the shift to twin scroll turbo. One thing was that they changed over from dual VANOS to a Valvetronic/VANOS combination when they made the N55. More advancements were made in the camshaft design to adapt to a single twin scroll turbo. The increase in pressure on the single turbo compared to two turbos requires a higher compression rate from the engine overall. Add to that a change in injectors used in the engine and it becomes clear that BMW did have to make some significant changes in their cars.

For BMW, they really needed to do this as twin-turbo set ups were less efficient and the twin-scroll turbo came in around the time they needed it as they used the twin-scroll turbo technology which originated from the N55 and applied it to the N20 engine, which was the twin-scroll successor to the NA N42 engine.

Therefore, BMW had means for production of twin-scroll turbo engines, as it provided significant advancement across a range of BMW's.

It can also be seen why some manufacturers never actually went to twin-scroll, due to limitations. The PH legend that is the Golf R Mk7 is surprisingly not a twin scroll turbo, again due to complexity and R&D issues. Then again, the EA888 is such a common engine in so many different forms, that they can't actually adapt the engine due to costs. If they were to make this a twin-scroll turbo, then the whole engine range would have to be modified, and there are many iterations of this engine in each different VAG group. Even the Audi TTS doesn't use it here. It still is impressive how they have managed 300hp out of a single scroll turbo engine. Even still, they were quite late to the game compared to BMW, and the size of the VAG means that there probably won't be this adaption due to costs.

Clearly, for VAG, quantity is put over quality unfortunately, as they have to adapt the same engine from the Golf R to go into a Tiguan, ultimately limiting the Golf R overall. If they had developed Twin-scroll turbo technology for this engine, the Golf R may well have much more than 300hp.

[rayyan171]

AW111 said:

279 said:

rayyan171 said:

It definitely is a cheaper and better alternative to adding 2 turbos instead as it puts less pressure on the block and produces less emissions, boost is at the highest and most efficient pressure so that helps too. It also saves on fuel as well.

Other manufacturers find it difficult to adapt because of the significant change in internals when changing from twin turbo to twin scroll. But, ford is using it and lexus too, so I am guessing other manufacturers will eventually catch on.

Could you please elborate a little more on the "significant change in internals" required for a twin scroll setup, and why they are required? I was under the impression that it is all in manifold and turbo design?

I can think of a few aftermarket applications where twin scroll turbos have been retrofitted to cars that used traditional turbos, through the use of specifically designed manifolds, seemingly with no issues.

Edited by 279 on Wednesday 7th December 02:30

I'm trying to work out what "boost is at the highest and most efficient pressure" means .

BMW used boost pressure at 8.8psi on the N54, the N55 ranged from 7-10psi. Varying the boost pressure means low pressure at low engine speeds, and high pressure at high engine speeds (boost on demand). The ECU is what varies the boost, so the engine is always at optimum boost.

[AW111]

rayyan171 said:

BMW used boost pressure at 8.8psi on the N54, the N55 ranged from 7-10psi. Varying the boost pressure means low pressure at low engine speeds, and high pressure at high engine speeds (boost on demand). The ECU is what varies the boost, so the engine is always at optimum boost.

Why would you want less boost at lower engine speeds? It sounds to me like they have given it a rising boost rate so it feels more like a n/a engine, at the cost of less mid-range power.

[rayyan171]

AW111 said:

rayyan171 said:

BMW used boost pressure at 8.8psi on the N54, the N55 ranged from 7-10psi. Varying the boost pressure means low pressure at low engine speeds, and high pressure at high engine speeds (boost on demand). The ECU is what varies the boost, so the engine is always at optimum boost.

Why would you want less boost at lower engine speeds? It sounds to me like they have given it a rising boost rate so it feels more like a n/a engine, at the cost of less mid-range power.

Low engine speeds are normally city speeds/stop-start driving, where high boost really isn't needed, but when the driver wants to accelerate, the engine does open up and provide more boost as RPM builds. The N55 did provide a 15% increase in efficiency while not losing power, alongside less turbo lag.

They have always never actually wanted forced induction on their cars, they've always wanted to make the engines feel NA.
Interestingly enough, the N55 did provide more mid-range power than the previous N54, showing that they really did do a lot of R&D into TwinPower Turbo technology, as it's ultimately their only option to continue. This is why BMW went from the S85 and S65 to the S63 and S55 engine for the M5 and M3, because it was their only way to significantly reduce emissions to prevent being shut down by European regulations. Even around the time of the S85 in the M5, Audi had to 'make do' with a twin turbo V10 to provide the power needed.

[Screechmr2]

Elysium said:

Twin beds are the same size. Twins are the same age. Identical twins are .. identical.

Wikipedia agrees with me (and I didn't edit it) as do many others. Ultimately both phrases are marketing terms and it can't be proven either way so there is no point in getting fussed about it.

https://en.wikipedia.org/wiki/Twin-turbo

I think twin turbo's are the same size and you don't. It's not a problem!

Edit: they couldn't agree on this in 2010 either:

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

Edited by Elysium on Sunday 4th December 17:13

i agree that 'identical twins' are the same but there are more than just identical twins, there are 'fraternal twins' and they aren't identical.

you're right we won't agree, so we'll have to agree to disagree. :-)