Why is a Twin scroll/Dual WG setup a benefit?

[TSi Kid]

I know someone's going to end up posting some links to the threads I could not find but oh well, I'll still ask.

I've been looking for some source of information of why a Twin scroll/Dual WG setup a benefit?

Anyone with just a basic explanation would be great.

 

[rlacasse1]

A twin scroll turbo will spool faster while maintaining the high end flow.

They require a dual wastegate setup because you have two separate ports that exhaust is flowing through. And if you combine those two exhaust flows then you have just defeated the purpose of the twin scroll. You have cylinders 1&4 that are going in one port of the turbine housing and you have cylinders 2&3 going in the other port on the turbine housing. They can not combine. Thus you have two wastegates.

 

[viprez586]

A twin scroll turbo will spool faster while maintaining the high end flow.

They require a dual wastegate setup because you have two separate ports that exhaust is flowing through. And if you combine those two exhaust flows then you have just defeated the purpose of the twin scroll. You have cylinders 1&4 that are going in one port of the turbine housing and you have cylinders 2&3 going in the other port on the turbine housing. They can not combine. Thus you have two wastegates.

You do not need two wastegates. A dual wastegate setup is only necessary for very high airflow & boost setups.
If you chose to run a external wastegate on a "scroll" designed manifold, you would need two(stupidly). Or simply run a O2 mounted external wastegate.

Answers.com - How does a twin scroll turbocharger work

A twin scroll turbine housing uses dual side by side passages into the housing. When coupled with a pulse converter manifold that separates exhaust pulses as many crank degrees in the firing order as possible, a twin scroll or divided housing works to reduce lag, decrease exhaust manifold backpressure on the top end, reduce the potential for reversion, and increase fuel economy. The twin scroll is based off the same reasoning a tri-Y header uses: keep spent exhaust gases out of an adjacent cylinder drawing in fresh air. At high rpm on a turbo car, exhaust backpressure is usually significantly higher than atmospheric pressure, and often higher than intake manifold pressure as well. A divider between each of the two volutes allows the cylinders to expel the exhaust gases without it interfering with the fresh air for combustion. Since there are two openings, each a smaller overall volume than a single scroll design, the exhaust velocity of each pulse can be maintained. This also spins the impeller more easily because lag is a function of the scroll area. A single turbine housing opening isn't as efficient since cylinders on the exhaust stroke of the 4 stroke cycle contaminate the cylinders that are on overlap with exhaust gas. A conventional turbine housing is not as effective in using exhaust pulse energy to help spin the turbine up to speed as it does not exploit the energy contained in the pulses as well.



Basically it works on the theory of cylinder exhaust scavenging/pulses.

 

[rlacasse1]

Rather than copying and pasting, why don't you explain to me what was wrong about what I posted. He asked for a simple explanation not an indepth discussion, and also explain how it was wrong.

The basic benefits are that it will spool quickly, like a smaller turbo. Yet flow well at the top end like a large turbo. And the double wastegates are just inherent.

 

[ViciousLord]

They require a dual wastegate setup because you have two separate ports that exhaust is flowing through. And if you combine those two exhaust flows then you have just defeated the purpose of the twin scroll. You have cylinders 1&4 that are going in one port of the turbine housing and you have cylinders 2&3 going in the other port on the turbine housing. They can not combine. Thus you have two wastegates.

Not true. If exhaust pulses are kept separate until wastegate opening a single wastegate will work just as good as a twin wastegate setup.

ex.
stock evo 9 hotside:

You must be logged in to view this image or video.

Borg Warner's EFR turbo with internal wastegate option.

You must be logged in to view this image or video.

 

[94_TSi]

Rather than copying and pasting, why don't you explain to me what was wrong about what I posted. He asked for a simple explanation not an indepth discussion, and also explain how it was wrong.

The basic benefits are that it will spool quickly, like a smaller turbo. Yet flow well at the top end like a large turbo. And the double wastegates are just inherent.

I think the small amount he wrote himself answers your question.

 

[rlacasse1]

So if you are trying to keep two exhaust flows separate and you use one wastegate how will that work at all? Because as soon as you throw in a single wastegate that has to release exhaust from both flows, you have just created an area for those two flows to interfere with each other. Which, seems to me like it would make the whoe twin scroll setup pretty useless.

I think the small amount he wrote himself answers your question.

It answers what?

Oh, not trying to start a fight here, but if I am seriously misunderstanding something then I would like to know.

 

[ViciousLord]

So if you are trying to keep two exhaust flows separate and you use one wastegate how will that work at all? Because as soon as you throw in a single wastegate that has to release exhaust from both flows, you have just created an area for those two flows to interfere with each other. Which, seems to me like it would make the whoe twin scroll setup pretty useless.



It answers what?

look at the pics... both exhaust pulses are kept separate until the wastgate opens. it's not hard to understand. The dividing metal seals both pulses against the wastegate opening, once the wastegate opens then yes the exhaust pulses will mix but will do so in the downpipe/O2 housing, outside the turbo/ manifold.

 

[dsmusmc]

If you want a shitty internal wastegate then you can use just one. If you want to be able to control your boost alot better then do the twin external wastegates. You could also run one off the o2 housing if you want a T3 or T3 with a bolt on outlet which no one makes unless you have an EVO but this is a DSM forum not an EVO forum.

 

[ViciousLord]

If you want a shitty internal wastegate then you can use just one. If you want to be able to control your boost alot better then do the twin external wastegates.

Not all internal wastegates are created equal. An internal wastegate works just fine on a stock evo 8-9 turbo... Every application has different requirements.

 

[rlacasse1]

Can't see the pictures, I'm at work, I will look after I get off.

And he asked about a dual wastegate setup, so it's going to be external. And there is no way for a single external wastegate keep the two flows from interfering til it is open.

Ok I just went Google searching and found manifolds similar to what I guess is posted above. I see how that could work. Before now I had never seen a manifold built for one wastegate and a twin scroll.

 

[dsmusmc]

Not all internal wastegates are created equal. An internal wastegate works just fine on a stock evo 8-9 turbo... Every application has different requirements.

Guess that would work if he was doing this for an EVO.

 

[ViciousLord]

And he asked about a dual wastegate setup, so it's going to be external. And there is no way for a single external wastegate keep the two flows from interfering til it is open.

Yes it can and will work. The fabricator has to design and build the manifold correctly. Will it be more labor intensive for the fabricator to build the manifold? Yes. But it will work. You just need to figure out if one wastegate will provide enough control. As I said before every setup has different requirements.

Ok I just went Google searching and found manifolds similar to what I guess is posted above. I see how that could work. Before now I had never seen a manifold built for one wastegate and a twin scroll.

Because building a proper TS manifold that uses a single wastegate is very labor intense.

You could also run one off the o2 housing if you want a T3 or T3 with a bolt on outlet which no one makes unless you have an EVO but this is a DSM forum not an EVO forum.

Guess that would work if he was doing this for an EVO.

But all turbos work on the same principal.

 

[rlacasse1]

Yeah, I just found pics of both a exhaust manifold that was made for twin scrol and using one wastegate. I see how it works, but looks like a b!tch to build. Then I saw a pic of a twin scroll turbine wastegate and once again understand how it works.

I was just confused as to how the single external would play out. Still doesn't look like it would be 100% effective in isolating the two. But I get the idea.

So OP, scratch what I said about the two wastgates being required.

 

[abaum565]

I know someone's going to end up posting some links to the threads I could not find but oh well, I'll still ask.

I've been looking for some source of information of why a Twin scroll/Dual WG setup a benefit?

Anyone with just a basic explanation would be great.

separating the exhaust pulses creates less backpressure, which results in more exhaust energy hitting the exhaust wheel. This results in better spool up while maintaining the "top end" of similar sizes turbos.

downside = cost!

 

[TSi Kid]

separating the exhaust pulses creates less backpressure, which results in more exhaust energy hitting the exhaust wheel. This results in better spool up while maintaining the "top end" of similar sizes turbos.

downside = cost!

So pulses and backpressure got it now, it's not that hard of a concept to understand once you get the concepts right .

I was just confused as to how the single external would play out. Still doesn't look like it would be 100% effective in isolating the two. But I get the idea.

So OP, scratch what I said about the two wastgates being required.

Yeah I saw that but I will still be goinig with two externals (agreeing with you), I want to max out that 258

 

[Shearer]

I know someone's going to end up posting some links to the threads I could not find but oh well, I'll still ask.

I've been looking for some source of information of why a Twin scroll/Dual WG setup a benefit?

Anyone with just a basic explanation would be great.

These threads give me a headache. They are usually filled with BS information and a lot of crap that someone read elsewhere on the internet and took it as fact. This is no different.

The fact of the matter is you will not find any evidence provided by the companies selling and marketing twin scroll manifolds & turbos that it works better than a standard turbo setup. IT DOESN'T. I've called out certain companies on their marketing BS for years and they still haven't come up with any data backing their claims.

The only reason we sell divided manifolds is simply because 90% of the turbos that we use in a T4 frame come with a divided housing from the turbo manufacturer.

Do divided manifolds have a purpose? Sure they do. On big displacement low RPM flat crank engines and OEM applications where emissions are a concern.

 

[jrohner]

The fact of the matter is you will not find any evidence provided by the companies selling and marketing twin scroll manifolds & turbos that it works better than a standard turbo setup. IT DOESN'T. I've called out certain companies on their marketing BS for years and they still haven't come up with any data backing their claims.
.

So spooling 500-1000+ rpms earlier isn't better?

 

[dsm-onster]

And every single auto manufacturer now using turbos with any application are using the much more expensive to fabricate twinscroll design. Most not using the "big displacement low RPM flat crank engines and OEM applications where emissions are a concern." Emissions affected by blowdown. When you have a turbo of which puts it's backpressure into the cylinder, you insert inert gases that fill a portion of the chamber, much like EGR.

Or perhaps you are saying that oem turbo applications can now get away with FAR more overlap with a turbo system that prevents blowdown from affecting overlap. Gases/charge get burned passing through the exhaust wheel, instead of bunching up in the cylinder during throttle. What's the point of more overlap again?

Marketing bs doesn't come from the originator of the twinscroll design. And it's silly to assume that preventing the blowdown event from ever at all affecting the overlap event of the subsequent cylinder would have NO effect at all. Just because YOU havn't found any proof doesn't mean that the rest of the modern automotive world hasn't.

How about this, the evo8 turbo (same as an evo 3 turbo but with a reverse scroll and twinscroll; even has the same a/r compressor housing with a different outlet mount) has net a higher mph vs. weight power output than the evo3 16g ever has.

Really, You should keep the personal issues with Full Race in the evom forums.

 

[ViciousLord]

Guys/Gals no need to get hostile or sarcasic. Everyone is entitled to there own opinion.

Everyone has certain preferences and every set up has different requirements.

Everyone has been gulity of being stubborn at times.

 

[dsm-onster]

Opinions are like. . .

Twinscroll setups are not a mandate for Emmisions Regulation, nor do they affect emmisions. I wonder why the evo has a twinscroll 16g turbo. . . . ????

 

[ViciousLord]

Opinions are like. . .

Twinscroll setups are not a mandate for Emmisions Regulation, nor do they affect emmisions. I wonder why The evo has a twinscroll 16g turbo. . . . ????

because it's proven to spool faster then any open/single scroll.

here's an old log from my evo 8 with a evo 9 turbo. I miss that bi***

You must be logged in to view this image or video.

33psi. right after 3500rpm... Stock bottom-end, Stock head with old school GSC 272s.

anyone have any logs of an evo 3 turbo? I'm curious to see how fast they spool compared to the evo 9 turbo.

 

[dsm-onster]

Exactly. And you didn't feel the need to put an open manifold on that thing. You can completely push the compressor to the limit with the faster spooling hotside with the same fuel as any evo3 16g setup has ever used.

The gearhead community is atuned to compromises and penalties. Benefit in one area, loss in another. All the "comparision tests" proving otherwise are those using twinscroll housings VERY small by twinscroll norm, or even more tiny: about the same collective a/r as the open housing control in the experiment. Yea the spool speed was 400rpms faster and the topend suffered. But what about a better chosen twinscroll housing? Maybe a 200rpm better spool and then still having the leverage of higher overlap potential, which when dialed in great contributes to spool speed AND increases topend.

None of the tests even accounted for the potential benefit of a cam retune. But who knows? One should go out and **prove the auto manufacturers of rally bred sports cars wrong**, not the other way around. but it's hard to have a good comparison test when one doesn't fully understand the concept behind the design. And those putting out those tests certainly have shown that.




This is as much of the same having your cake and eating it too as a better compressor wheel or turbine wheel. It prevents energy from being lost in blowdown to the next firing cylinder. Energy saved much like a wheel is more efficient (energy saved instead of being turned to heat or wasted in the exhaust).

 

[ViciousLord]

Exactly. And you didn't feel the need to put an open manifold on that thing. You can completely push the compressor to the limit with the faster spooling hotside with the same fuel as any evo3 16g setup has ever used. The gearhead community is atuned to compromises and penalties. Benefit in one area, loss in another. This is as much of the same having your cake and eating it too as a better compressor wheel or turbine wheel. It prevents energy from being lost in blowdown to the next firing cylinder. Energy saved much like a wheel is more efficient (energy saved instead of being turned to heat or wasted in the exhaust).

I did have the Full-Race pro-stock manifold

 

[wishihadatalon]

And every single auto manufacturer now using turbos with any application are using the much more expensive to fabricate twinscroll design. Most not using the "big displacement low RPM flat crank engines and OEM applications where emissions are a concern." Emissions affected by blowdown. When you have a turbo of which puts it's backpressure into the cylinder, you insert inert gases that fill a portion of the chamber, much like EGR.

Or perhaps you are saying that oem turbo applications can now get away with FAR more overlap with a turbo system that prevents blowdown from affecting overlap. Gases/charge get burned passing through the exhaust wheel, instead of bunching up in the cylinder during throttle. What's the point of more overlap again?

Marketing bs doesn't come from the originator of the twinscroll design. And it's silly to assume that preventing the blowdown event from ever at all affecting the overlap event of the subsequent cylinder would have NO effect at all. Just because YOU havn't found any proof doesn't mean that the rest of the modern automotive world hasn't.

How about this, the evo8 turbo (same as an evo 3 turbo but with a reverse scroll and twinscroll; even has the same a/r compressor housing with a different outlet mount) has net a higher mph vs. weight power output than the evo3 16g ever has.

Really, You should keep the personal issues with Full Race in the evom forums.

I think you are a little quick to claim that the time differences between an evo3 16g dsm and an evo 8 16g evo are because of the turbo. Evos have a decade of engineering and technology in their favor (mostly in the cylinder head).

The only question I will ask is this. Is a twin scroll design a band aid for a poorly designed oem exhaust manifold due to extremely tight space constraints found in todays engine bays? It seems that people using properly designed manifolds (gradual taper at the collector, equal length, ect.) are seeing really good spool characteristics in the evo world.

Edit*
I realized that "poorly" was probably the wrong term to use above. I was mearly stating that comprimises must be made by engineers to make anything they design work.