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

 

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..

 

Er, what he said! (Thanks Nathan!)

It's neither, if we're being strictly accurate. It's not a Spec C, and it's definitely not (and never was) a Type UK

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.

 

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.

 

Does this mean that equal length headers lose the much loved 'burble'?

 

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.

 

I love my burble!

 

I doubt you'll miss it when you hear how the new cars sound. Much more like the WRCars.

 

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..

 

Hmmm! Can't I have both?

 

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

 

Is it the same jet fighter, or 'hoover' sound, that powers the Evos?

 

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

 

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

 

Lol, Mitsi have used twin scroll turbos for years. Evo IV definitely did, and I think it might have gone even further back than that!

 

LOL I thought as much, was having a blonde moment

 

someone told me my03 wrx has a twin scroll td4 in it is this true?

 

No !!

 

No. The only Imprezas with twin scroll turbos are the Japanese market STi's (and their export derivatives like the Type 25).

 

Bob, not "EVO's don't sound anyting like as good.", but "EVO's can't sound anyting like as good."

Richard