Twin Scroll Turbo & Type 25
15 April 2004, 09:12 PM
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Twin Scroll Turbo & Type 25
Firstly can someone please explain to me the differences between a twin scroll turbo and a normal one and what advantages if any they have?
Secondly, Is powerstations Type 25 based on a Spec C or a UK sti modified to be the same as the Spec C aside from the engine?
Thanks
Secondly, Is powerstations Type 25 based on a Spec C or a UK sti modified to be the same as the Spec C aside from the engine?
Thanks
15 April 2004, 09:58 PM
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Copyright 'Greasemonkey' ;)
The twin scroll turbo/equal length 4:2 header setup increases turbo efficiency over the single scroll/ unequal length 4:1 header used by most Subarus in a number of different ways.
The hotside of the turbo has two separate gas inlets. The exhaust manifolds, instead of being combined into a single up-pipe, are combined into two, with the twin up-pipes keeping the gas from adjacent (in firing order) cylinders separate all the way up into the turbo, where the twin scroll exhaust housing separates them all the way onto the turbine blades.
The first advantage is that the equal length design of the headers evens out the time intervals with which the exhaust gas pulses hit the turbine blades. This imparts more energy into the turbo, which helps promote quicker spool.
The second advantage is that the separation of adjacent gas pulses in the headers and turbo prevents something called reversal, which is where part of the gas pulse takes a "wrong turn" in the normal manifold, and starts travelling back towards the other cylinders instead of to the turbo, where it can collide with the next gas pulse, reducing the energy available to drive the turbine round in the process. By virtually eliminating this, you're again getting more energy into the turbine blades rather than wasting it.
The increases in turbine efficiency mean a smaller one can be used for any given size of compressor and desired flow rate, and the reduction in size leads to a reduction in rotating mass, which again helps spool and response.
Another happy advantage of the lack of reversal is that the knock-on effects can improve fuel efficiency, so it's an improvement all round.
AFAIK the T25 can is based on either a Spec C or a JDM STi GL. The choice is yours.
Nathan..
The hotside of the turbo has two separate gas inlets. The exhaust manifolds, instead of being combined into a single up-pipe, are combined into two, with the twin up-pipes keeping the gas from adjacent (in firing order) cylinders separate all the way up into the turbo, where the twin scroll exhaust housing separates them all the way onto the turbine blades.
The first advantage is that the equal length design of the headers evens out the time intervals with which the exhaust gas pulses hit the turbine blades. This imparts more energy into the turbo, which helps promote quicker spool.
The second advantage is that the separation of adjacent gas pulses in the headers and turbo prevents something called reversal, which is where part of the gas pulse takes a "wrong turn" in the normal manifold, and starts travelling back towards the other cylinders instead of to the turbo, where it can collide with the next gas pulse, reducing the energy available to drive the turbine round in the process. By virtually eliminating this, you're again getting more energy into the turbine blades rather than wasting it.
The increases in turbine efficiency mean a smaller one can be used for any given size of compressor and desired flow rate, and the reduction in size leads to a reduction in rotating mass, which again helps spool and response.
Another happy advantage of the lack of reversal is that the knock-on effects can improve fuel efficiency, so it's an improvement all round.
AFAIK the T25 can is based on either a Spec C or a JDM STi GL. The choice is yours.
Nathan..
15 April 2004, 10:12 PM
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Originally Posted by MiGi
Firstly can someone please explain to me the differences between a twin scroll turbo and a normal one and what advantages if any they have?
(Thanks Nathan!)
Secondly, Is powerstations Type 25 based on a Spec C or a UK sti modified to be the same as the Spec C aside from the engine?
The cars seem to arrive in this country as Japanese specification standard weight STi "GL's", as Nathan says, complete with the electric windows, climate control and all the other normal toys that the lightweight cars lack. From that base car the engine, suspension and other changes are made to uprate to Type 25 specification.
I've not seen anything on Iain's website or here to indicate that the car can be purchased built on a Spec C donor car (or in a similar ultra-lightweight, no frills configuration) as Nathan suggests, but there doesn't seem to be any specific reason why this couldn't be done if you wanted a car built this way, and were prepared to shell out for it.
15 April 2004, 11:05 PM
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I spoke to Iain @ Powerstation whilst I was having my STi 9 GL HID's looked at, he said if you wanted a T25 built onto a Spec C it wouldn't be a problem.
Now that would be a little bit quick
Nathan..
PS I cut'n'pasted your explanation as its about the easiest I have seen to follow.
Now that would be a little bit quick
Nathan..
PS I cut'n'pasted your explanation as its about the easiest I have seen to follow.
15 April 2004, 11:44 PM
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Originally Posted by Nathan L
The twin scroll turbo/equal length 4:2 header setup increases turbo efficiency over the single scroll/ unequal length 4:1 header used by most Subarus in a number of different ways.
The hotside of the turbo has two separate gas inlets. The exhaust manifolds, instead of being combined into a single up-pipe, are combined into two, with the twin up-pipes keeping the gas from adjacent (in firing order) cylinders separate all the way up into the turbo, where the twin scroll exhaust housing separates them all the way onto the turbine blades.
The first advantage is that the equal length design of the headers evens out the time intervals with which the exhaust gas pulses hit the turbine blades. This imparts more energy into the turbo, which helps promote quicker spool.
The second advantage is that the separation of adjacent gas pulses in the headers and turbo prevents something called reversal, which is where part of the gas pulse takes a "wrong turn" in the normal manifold, and starts travelling back towards the other cylinders instead of to the turbo, where it can collide with the next gas pulse, reducing the energy available to drive the turbine round in the process. By virtually eliminating this, you're again getting more energy into the turbine blades rather than wasting it.
The increases in turbine efficiency mean a smaller one can be used for any given size of compressor and desired flow rate, and the reduction in size leads to a reduction in rotating mass, which again helps spool and response.
Another happy advantage of the lack of reversal is that the knock-on effects can improve fuel efficiency, so it's an improvement all round.
AFAIK the T25 can is based on either a Spec C or a JDM STi GL. The choice is yours.
Nathan..
The hotside of the turbo has two separate gas inlets. The exhaust manifolds, instead of being combined into a single up-pipe, are combined into two, with the twin up-pipes keeping the gas from adjacent (in firing order) cylinders separate all the way up into the turbo, where the twin scroll exhaust housing separates them all the way onto the turbine blades.
The first advantage is that the equal length design of the headers evens out the time intervals with which the exhaust gas pulses hit the turbine blades. This imparts more energy into the turbo, which helps promote quicker spool.
The second advantage is that the separation of adjacent gas pulses in the headers and turbo prevents something called reversal, which is where part of the gas pulse takes a "wrong turn" in the normal manifold, and starts travelling back towards the other cylinders instead of to the turbo, where it can collide with the next gas pulse, reducing the energy available to drive the turbine round in the process. By virtually eliminating this, you're again getting more energy into the turbine blades rather than wasting it.
The increases in turbine efficiency mean a smaller one can be used for any given size of compressor and desired flow rate, and the reduction in size leads to a reduction in rotating mass, which again helps spool and response.
Another happy advantage of the lack of reversal is that the knock-on effects can improve fuel efficiency, so it's an improvement all round.
AFAIK the T25 can is based on either a Spec C or a JDM STi GL. The choice is yours.
Nathan..
15 April 2004, 11:52 PM
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Yes. It's replaced by a harder edged snarl/howl that is much less intrusive under cruise conditions, and, IMO at least, is very fine indeed. Don't miss the "burble" at all.
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16 April 2004, 10:15 AM
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Hugo
My STi 9 with these new tubular headers and an HKS Super Drager has been described as sounding like a jet fighter and an exocet missile under full chat.
I loved the burble of my old MY01 but I also love the growl and sudden raspiness of this exhaust too.
Nathan..
My STi 9 with these new tubular headers and an HKS Super Drager has been described as sounding like a jet fighter and an exocet missile under full chat.
I loved the burble of my old MY01 but I also love the growl and sudden raspiness of this exhaust too.
Nathan..
17 April 2004, 09:42 AM
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Both? 
When you hear the difference you will think "god that sounds rough" (stating the older/uneven manifold models) but then you will think "ohhhh jet fighter" because as Nathan stated, it does sound like one
Tony
When you hear the difference you will think "god that sounds rough" (stating the older/uneven manifold models) but then you will think "ohhhh jet fighter
" because as Nathan stated, it does sound like one Tony
17 April 2004, 11:41 AM
#13
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Someone likened mine on full chat to a V6 engined car, certainly you can still hear the faintest hint of burble on idle, on full chat though its really something on its own. EVO's don't sound anyting like as good.
bob
bob
17 April 2004, 01:45 PM
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Ahh I see, not as much to it as I thought, which is nice. Are mistubushi using this type of turbo on their evo's? Or is this a newish concept from subaru? Just wondering.....
I like the burble, but happily swap for more power
I like the burble, but happily swap for more power
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