twin scroll turbo...

how do they work, what do they do?

i've heard of them, know they were first used on the lancer evo (i think it was the evo III)...

any info would be great, it's one of the few things that i can't get my head around, and i've looked everywhere...

A turbine section of a turbocharger with separate inlets for separate headers... e.g. a twin-scroll turbo could be used with two 3-1 headers (on a V-12, say).

I suppose they make for less exhaust restriction/backpressure.

missed this one, the twin scroll is all about tuning, it keeps one exhaust pulse from reversing back to the head. Like a log manifold for example, shitty tuning since all the exhaust feeds into 1 log, a twin scroll lets a V6 or 8 stick 1 pair of header primaries into one side without worrying about the pulse from another reversing back up it, very good setup to use.

so it's basically like putting a turbo on the end of the first section of a header...

where it goes 4 into 2...

i figured it would be more complex than that...

thanks guys

Originally posted by flylwsi
so it's basically like putting a turbo on the end of the first section of a header...

where it goes 4 into 2...

i figured it would be more complex than that...

thanks guys
What?

LOL

now i'm back to square one, b/c i'm pretty sure that neither post really explained anything here after rereading what was posted.

especially considering that i replied to 454 with the exact same thing he said.

any other takers to help me out?

the twin scroll is just a more advanced tubine housing design that helps to enhance exhaust gass energy utilization while minimizing ehxaust manifold backpressure and hence potential for reversion.

Think of your average inline 4 cylinder. Ever notice how in 4-2-1 headers they always pair cylinder 1 with 4 and cylinder 2 with 3 when merging the 4 pipes into the 2 secondaries? The basic firing order dictates that pairing these cylinders together will give the longest possible gap between exhaust pulses traveling through the pipes, thus enhancing flow while minimizing reversion. The twin scroll operates with the same basic principle in mind: keep the cylinders firing into an exhaust pipe that isn't already stuffed full of exhaust from an adjacent cylinder. With turbo cars this can be especially important as at higher RPM exhaust backpressure is usually significantly higher than atmospheric pressure, and often higher than intake manifold pressure as well.

So the twin scroll creates two exhaust paths instead of one, allowing for that increased separation in exhaust flow that is key to keeping everything from stacking up behind the turbo and causing reversion. It also helps to preserve the exhaust velocity of each pulse by offering a smaller overall volume to hold each one, so the turbine impeller is more easily spun up by a given total amount of flow than an equivalent single scroll design. Or at least that's the theory behind them. Answer your questions?

thanks, so i was right in thinking that it would be like putting a turbo onto a header where it merges 4-2, right?

that makes sense...

Yes, that would be an accurate way to describe it.

good, b/c that's what i said earlier, and the people who replied seemed a little dumbfounded.

thank you texan.

Originally posted by flylwsi
good, b/c that's what i said earlier, and the people who replied seemed a little dumbfounded.

thank you texan.
It's just that I didn't understand you. Maybe if you said "2-1 headers".

but it's not 2 into 1.

it's where the 4 tubes go into 2.

where it goes 4 into 2...

which is what i said...

it's where the first Y's are at in the header setup, regardless of being 4 cyl, or 6...

so on a 4 cyl (or one side of a v8) it's where the 4 go into 2.

I'm glad I didn't say anything earlier in this post, because I misread the question initially. I was going to describe a two-spool turbo, not a "twin-scroll" turbo. Completely different.

since you brought it up... what's a dual spool turbo?

one with two turbine stages driving two compressor stages via concentric shafts. Somewhat similar to the compressor and turbine stages on a gas turbine engine.

I don't think they're in use in vehicular applications at this point, but perhaps in 5-10 years.

I may be wrong but are you sure your not confusing twin entry with twin scroll ? What you have described to me here sounds like twin entry.

Twin scroll as I understand it -
The scroll area dictates lag, the larger it is the more it flows up top but the more laggy it is. At low rpm's there is less exhaust gasses flowing out the exhaust and hence is harder to spin the turbo, so a smaller port is used (only one of the exhaust ports are open), after a certain rev range or boost range, an actuator opens the second exhaust port to the turbo allowing more gases to enter and spin the turbo.

The idea of the twin scroll is to minimize turbo lag.


As I said, I may be wrong .....


Originally posted by texan
the twin scroll is just a more advanced tubine housing design that helps to enhance exhaust gass energy utilization while minimizing ehxaust manifold backpressure and hence potential for reversion.

Think of your average inline 4 cylinder. Ever notice how in 4-2-1 headers they always pair cylinder 1 with 4 and cylinder 2 with 3 when merging the 4 pipes into the 2 secondaries? The basic firing order dictates that pairing these cylinders together will give the longest possible gap between exhaust pulses traveling through the pipes, thus enhancing flow while minimizing reversion. The twin scroll operates with the same basic principle in mind: keep the cylinders firing into an exhaust pipe that isn't already stuffed full of exhaust from an adjacent cylinder. With turbo cars this can be especially important as at higher RPM exhaust backpressure is usually significantly higher than atmospheric pressure, and often higher than intake manifold pressure as well.

So the twin scroll creates two exhaust paths instead of one, allowing for that increased separation in exhaust flow that is key to keeping everything from stacking up behind the turbo and causing reversion. It also helps to preserve the exhaust velocity of each pulse by offering a smaller overall volume to hold each one, so the turbine impeller is more easily spun up by a given total amount of flow than an equivalent single scroll design. Or at least that's the theory behind them. Answer your questions?

Originally posted by gtpornstar
I may be wrong but are you sure your not confusing twin entry with twin scroll ? What you have described to me here sounds like twin entry.

Twin scroll as I understand it -
The scroll area dictates lag, the larger it is the more it flows up top but the more laggy it is. At low rpm's there is less exhaust gasses flowing out the exhaust and hence is harder to spin the turbo, so a smaller port is used (only one of the exhaust ports are open), after a certain rev range or boost range, an actuator opens the second exhaust port to the turbo allowing more gases to enter and spin the turbo.

The idea of the twin scroll is to minimize turbo lag.


As I said, I may be wrong .....



I've never heard of that which you describe, but it does sound like it would be effective.

However, when I first read that, I thought you were talking about a standard twin-scroll turbine /w variable-area entry ports. That would have the benefits of less backpressure (due to the separate entry), and the variable size of the entry ports allow the velocity of a lower volume of exhaust gas to increase (increasing low-RPM efficiency).

Actually that is what I was trying to explain :rolleyes: :)

Actually that is what I was trying to explain :rolleyes: :)
Variable vane turbos pretty much do what we were discussing.

The name "twin scroll" is used for both "twin entry" and "variable entry ports".

http://www.egarrett.com/technology/tech_twin_scroll.jsp?justlist=1&l1id=2&l2id=2&l3id=1

The name "twin scroll" is used for both "twin entry" and "variable entry ports".

http://www.egarrett.com/technology/tech_twin_scroll.jsp?justlist=1&l1id=2&l2id=2&l3id=1
I don't see anything in that page that refers to variable entry...

I don't see anything in that page that refers to variable entry...

That's because there aren't any info on that page about variable entry.

But what it does explain is what twin scroll means, twin scroll is just a diffrent name for twin volute or in the case of turbine houses twin inlet (in the compressor the volute is the outlet). The use described on that page is the most common but it can of course be used to vary the inlet speed into the turbine, however since we have VNT we can use that instead, which I think is also a much better technology.