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Discussion Starter #1
Here's how it works.

By Kristen Lee, Dec 16, 2015

Turbocharging technology has come a long way, becoming more and more efficient with time. Engineering Explained goes in depth to explore a new type of turbo that BorgWarner showcased at SEMA.

While the tech for a variable twin scroll turbo has been in existence for ages, it's now on the way to ubiquity with all the new emissions and efficiency regulations. It might be the best way to get that extra power while still meeting the law of the land.

If you're curious as to how twin scroll turbochargers and variable geometry turbochargers work, check out these three videos. It'll make much more sense to you afterwards if you're stuck.




Is Variable Twin Scroll Turbocharging the Answer to Future Turbos?
 

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It is about time this became main stream with automobiles. Dodge did this in the 80's (not completely successfully) and this will allow a turbocharger to provide more area under the curve with low end torque and high end torque. Couple this with hydraulic assist and it is game on!
 

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Discussion Starter #5 (Edited)
Isn't this the same guy from the Don't Buy a STI video?


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VGT twin scroll turbos are a great idea. There are some drawbacks though. They are expensive and they eventually develop reliability issues. Particulate emissions are also a big concern(checkout Ford's powerstroke turbo problems) which typically isn't that big of a concern with gas engines but GDI it is a little more prone to deposits.
 

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Similar concept, but without the advantages of twin-scroll routing.
The advantage of twin scroll manifold routings is primarily reducing spool time but it is restrictive for peak power production. Spool valves have been proven to produce similar results to full twin scroll systems with the peak power benefits of a open scroll system. Nice to see this tech potentially making it into oem applications but the concept has been around for awhile.
 

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The concept was designed into the 1986 Sierra Cosworth exhaust manifold by for the RS500's to run twin scoll turbos.
IMG_20110811_203332.jpg
 

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The concept was designed into the 1986 Sierra Cosworth exhaust manifold by for the RS500's to run twin scoll turbos.
View attachment 3025
Unfortunately Garrett never made a twin scroll T3 turbine housing so it was a somewhat wasted design. Holset was probably the only manufacturer at the time to produce a T3 footprint twin scroll housing.
 

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The RS500 ran a T4 Turbo, the base model, Cosworth RS used the T3. The manifold was stock on both.
 

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The RS500 ran a T4 Turbo, the base model, Cosworth RS used the T3. The manifold was stock on both.
Technically the RS500 had a hybrid t3/4 turbo. The compressor side was T4 but the exhaust side was a T3 stage III wheel and housing which is why it used the same footprint on the manifold. A true T4 would have a larger, square shaped inlet flange on the turbine housing.
 

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T4 isn't a direct bolt on the stock 2wd manifold. But have to use the rare T4 trouser leg, was made for Group B racing I guess. But still nice to have the divided twin scroll manifold.
003.jpg
 

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Yes the dropped bracket is required to clear the larger diameter of the T4 compressor housing. The RS500 turbo is known in the Cosworth community as the "T4" turbo but it is not truly a T4, a true T4 exhaust housing is massive and by today's standards it looks out of proportion compared to the compressor.
 

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T4 isn't a direct bolt on the stock 2wd manifold. But have to use the rare T4 trouser leg, was made for Group B racing I guess. But still nice to have the divided twin scroll manifold.
View attachment 3032
Atp and Agp both make Garrett t3 twin scroll exhaust housings for those who want to take advantage of the original design as it was intended. Tbh the T4 designs are dinosaur technology, much better options in the Gt/Gtx line up.
 

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I agree on the T4 being Old School....very old school. I'm currently running a T38 but have thoughts on later upgrading.

Thanks for you input.

PS. Love to see pics of you RS500 replica, specs? PM not wishing to thread jack
 

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Pm sent
 

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Isn't this the same guy from the Don't Buy a STI video?


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That's Jason, he runs this channel "Engineering Explained" where he describes all sorts of car-related things, as well as does some car reviews. Great videos! I'm a big fan of his.
 
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