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Discussion Starter #1
First of all, do we have a forum search capability? I clicked on the seach part of the "Modules" but it didn't appear to search the forum.

In any event, I remember reading about the twin scroll turbo, before the 2.5L was announced. Interesting concept. It would also seem to decrease turbo lag by making the turbo more efficient? Also would lag be reduced by simply making the exhaust inlet pipe the shortest amount possible? Or does it matter how much volume of air is available to the intake side of the turbo?

Anyone wanna go over the ins and outs of turbo lag for an inept fool? :)

http://www.cmmstudio.com/G2001/g-innovate_tsth.html
Garrett Twin Scroll design, sorry if its already been posted.
 

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I am no guru of turbo knowledge, but I do know that turbo lag is the time you have to wait for your turbo to spool up ( varies on cars, usually from 2k-4k RPMs) The Evo has the twin scroll so that the turbo spools up faster to reduce lag. The Sti, on the other hand, does not use the more expensive twin-scroll turbo because it has dealt with the problem in another way. The 2.5 liter boxer engine supposedly has much more low end torque than the Evo 2.0, which will compensate for the turbo lag. I dunno, you may have known this much already :lol:
 

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According to the official specs, the peak torque is at 4000 rpm. This is the same rpm as the WRX so I would guess it would have similiar turbo lag characteristics. I have not driven a WRX but I have heard it has decent amount of turbo lag. My turbo charged A4 has peak torque starting at 2k up to I think 4k and I still notice the lag:)

Hopefully the variable valve stuff will help reduce it on the STi. Of course you can just look at it as a challenge to driving your STi better :D

Jeff
 

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I'm certainly no turbo guru, but the twin-scroll turbo was designed to give more torque at the lower end, nearly reducing major turbo lag. Turbo lag is just the time needed for the exhaust gases to spool up the turbine inside the turbo's housing. The higher rpms the more exhaust gases flow and push the turbine fins faster/harder. Each turbo is different and the angle of the turbine fins have a lot to do with when peak turbo rpm (not engine rpm) is reached. At higher turbo rpms higher boost is generated. So, from what I can tell the twin-scroll more efficiently uses the available exhaust gases in order to reach desired boost levels on the turbo.

Correct me if I am wrong, just trying to lend a helping hand. :)
 

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91TB78 said:
I'm certainly no turbo guru, but the twin-scroll turbo was designed to give more torque at the lower end, nearly reducing major turbo lag. Turbo lag is just the time needed for the exhaust gases to spool up the turbine inside the turbo's housing. The higher rpms the more exhaust gases flow and push the turbine fins faster/harder. Each turbo is different and the angle of the turbine fins have a lot to do with when peak turbo rpm (not engine rpm) is reached. At higher turbo rpms higher boost is generated. So, from what I can tell the twin-scroll more efficiently uses the available exhaust gases in order to reach desired boost levels on the turbo.

Correct me if I am wrong, just trying to lend a helping hand. :)
Thats the way I understand it too.

Also I think in general, the larger the turbo the larger the lag. Smaller the turbo, less the lag. This assumes a non twin-scroll turbo.
 

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You dont just add it to the 2.5. It isn't that easy. Personally I will just add the 2.2L stroker kit to my 4G63 and make way more torque than the STI can dream of. The Evo already has a long stroke to bore ratio and the JUN 2.2 kit adds even more. When combined to a proven twin scroll designed turbo the torque band is suppose to be unmatched by anything less than a six cyl or twin turbo.
 

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true..i think that's why you see WAAAYY too many arguments and crap online. No one can sense tone very easily.

Hey, so if you do the 2.2 Jun stroker kit to the 4G63 why would that make more torque than the 2.5 (given the same amount of boost...hypothetically)? I mean you're still looking at 300ci of displacement above the stroker kit, and I thought bore was more influential to torque increase.
 

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///M3anMachine said:
I am no guru of turbo knowledge, but I do know that turbo lag is the time you have to wait for your turbo to spool up ( varies on cars, usually from 2k-4k RPMs)
Just to clarify as the terms are interchanged often and it's rare that the difference is pointed out:

"Boost threshold" is the lower RPM limit (not a time at all) that a turbo car needs to be above to be able to produce positive boost. This is what you are feeling from a dead stop when you floor the car and "wait for the turbos to spool." It is *not* turbo lag. You can have a lag-free turbo car and still have a significant boost threshold.

"Turbo lag"- which is a term that's misused a lot- is the time it takes (not RPMs, mind you) for a car already cruising at negative boost and above the boost threshold to produce positive boost after you mash the go-pedal. Turbo lag is something that affect driveability and responsiveness. Less lag == more responsive engine.

-Alt
 

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Porsche 911 Turbo versus STI Site

Jeff_DML said:
According to the official specs, the peak torque is at 4000 rpm. This is the same rpm as the WRX so I would guess it would have similiar turbo lag characteristics
Just because the peak torque is at 4000 rpm in both cars, that doesn't tell you the shape of the torque curve...I'd imagine that the torque curve would be steeper in the STi.
 

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Steeper? I'd expect it to be shallower... more plateau-like due to the added displacement and lower boost pressure (for the same specific output as the 2.0 at least).

-Alt
 

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yeah im also hoping for a really flat torque curve like 260 torque from 2K rpm that would be sweet :) who knows though but i definitely want to see those specs....
 
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