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Discussion Starter #1 (Edited)
As the title said, I now have IHI VF56 turbo from WRX STI R205, which means equal length manifold.

And I will get to the point; it does not drone. Not in this setup.


Straight forward conversion; no fuss

Parts installed:
1. IHI VF56 turbo from WRX STI R205
2. OEM twin scroll exhaust manifold + uppipe
3. HKS twin scroll downpipe with dual catalytic converter
4. Tomei turbo inlet


it fits just nice. And thanks to HKS donut gasket, the seal is properly tight

Here are the differences between different setup:
1. All stock + Corsa catback = eerily quiet inside the car, but good loudness outside. I keep wanting to hear the sound of the exhaust but to do so I had to drive with windows open. It is that quiet inside the car. Drone is non existence.

2. All stock + Corsa catback + 3inch catted downpipe = now there is good sound volume inside the car, no need to roll down the window just to hear. But just as the sound volume increases inside the car, the outside sound became very loud. Some will find this intrusive, and that is understandable, but because it sounds really awesome it can also receive a forgiveness of being very loud. Still, there is no drone despite the increase of volume.

3. VF56 twinscroll setup + Corsa catback + HKS dual cat twin scroll downpipe = superior in everyway. In short, it is the balance between setup no. 1 and setup no. 2, and like setup 1 and 2 = there is no drone.


But how does it actually sound? Well, it is hard to describe it, but I am glad to report it does not sound like a Honda. From outside It sounds deep, and even cleaner than all stock + Corsa catback. The burble is still there, but much less of it.

When driving, and so far I have to behave and stay in Intelligent mode to keep me off from boost, the sound is very pleasing. Very hollow and high flow, no high pitch and no excessive loudness. So instead of telling you all how it sounded, a video will come soon (cold start, warm idle, off boost driving, and interior).

I personally like the sound of this setup more than the UEL single scroll setup; because as it turns out the cool Subaru burble is still there, except now it sounded much smoother and high flowing. I surely hate it if its going to sound high pitch, but instead I got a deep sounding exhaust. In my mind, it is the HKS downpipe that plays a big role to result in this sound; due to its dual cat. And HKS have followed strict JDM emission regulation both in sound and emission. In many ways the sound reminded me of my previous car, ZZT231 Celica with TRD Response S muffler. It is very deep, very clean and very high flowing without the high pitch buzz saw sound most associated it to being a Honda sound.

Then again, I am sure my twinscroll setup have a direct impact on the overall sound.
 

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Discussion Starter #2 (Edited)
And, some photos of my Corsa catback condition...in particular the resonator.


The problem...


The aftermath...


Hmmmm...maybe I should consider replacing that resonator.
 

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Discussion Starter #3
As promised:

Corsa with VF56: Warm idle, normal driving on Intelligent mode, and interior recording.

Corsa with 3' catted downpipe

Corsa catback only

The GoPro is rather boomy, but anyhow you guys can be the judge.

Of course, I do not know what it will sound like once I can go all out, but suffice to say for daily driving this is just perfect. Sound wise, it is definitely not as growly, but I am quite surprised it still sound very similar.
 

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Discussion Starter #5
The cold start recording was recorded using Sony action camera with Rode external mic.

Overall, I am very glad my car did not get any louder but instead it gets mellower. Great tone and no drone.

Once my car is tuned (should be next week), I will post a full throttle video.
 

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Discussion Starter #6
So I like to go off-topic now, and talk about the VF56 turbo setup. Since it is a simple enough conversion, I don't think it is worth a new thread. I mean, it isn't exactly something that is worth to start a build thread for.

And maybe there are some who are interested in converting to jdm twinscroll for JDM setup for their GR/GV but not sure of what is involved. Still, this kinda of conversion isn't new as it has been done many times on previous model, and in short it isn't any different to the GR/GV model. But there are things to know to do it right.

Required Parts
1. JDM turbo; VF56, or VF53, or VF49. IHI Turbo listing - ART Performance
2. JDM twinscroll manifold. (any year model will do)
3. Twinscroll turbo bracket
4. Twinscroll turbo heat shield
5. Twinscroll oil feed line. Note: VF56 and VF53 are both ball bearing turbo and it has a different oil feed line part number to VF49 (thrust bearing) oil feed line, and if I recall the VF49 has the same part number to VF42 (roller bearing) oil feed line.
6. Twinscroll turbo water hose
7. Twinscroll downpipe for GRB/GVB (I will share more about this below).



A little bit of background about my car and why I went for this conversion and specifically chosen VF56.

I've owned the car for a few years now, and in general I really like my STI. I didn't do much for the engine, just turbo-back exhaust, stage 2 tune and cooling mods. I did quite a bit of suspension mods to make it ride and handles to my liking. And everything are well.


But I have a friend who keep reminding me to get a JDM STI twinscroll turbo.

I have mentioned it a few times in this forum of how I once tried my friend's 2008 2.5L STI with IHI VF42 turbo, and that car has an amazing engine response all the way from low rpm to redline. From one gas pedal to another, the engine immediately responded; just like N/A engine. I really like that from an engine, and if I have to change the turbo it will have to be VF42 or better so my engine is as responsive as that 2008 2.5L STI with VF42.

I then founded out the Legacy S402, a special edition model with 2.5L and twinscroll turbo.


Looking at that torque curve confirmed my experience of driving my friend's 2008 2.5L STI with VF42. I used to have the graph for R205 power curve, and while on paper it stated max torque is achieved at 4000rpm, what the power curve showed is by around 2500rpm it is already making about 80% of max torque. Impressive.

But there is a problem; VF42 is rare to begin with and used ones are high in mileage. By now Subaru has moved on to VF56, but I read to get this turbo I have to supply VIN number. True or not, I do not know. VF53 for GRB Spec C is available, but unlike VF56 it does not use titanium compressor wheel. So I put this twinscroll conversion into the back burner and never put much thought about it.

Until sometimes around July this year, out of the blue I found a brand new VF56 for sale.

And here it is, my IHI VF56.


The next step is to get the missing pieces, and this is the area where things went grey at the beginning. For me, at least.

My friend told me he had to modify his catback, and Toronto Subaru forum who installed VF37 into his 2015 said he too had to modify his catback. I quickly figured it out, both my friend and the Toronto Subaru member were using twinscroll downpipe from GDB STI. I thought I had it all solved and all I had to do is to get myself a JDM downpipe for GRB/GVB - until I saw on HKS website that their GRB/GVB downpipe is "impossible" to fit to S206. I can't even find the HKS e-mail to ask why is it impossible. Is it due to the difference in turbo downpipe flange, or is it a difference of midpipe length?

I cross checked a few JDM catback, and my finding was the catback will fit both GRB/GVB and GRF/GVF. So no different in catback, but still no answer as to why can't the HKS downpipe fits S206.

Now the reason why I was looking at S206 was because I thought the VF56 is the turbo on S206. But looks like that is not the case, at least by the finding of Russian Subaru owner the S206 uses VF58.


Well, I cannot argue with that. It is clearly a VF58.

So back to HKS web and I found out HKS stated their downpipe for GRB is not 'applicable' for R205. Oh great, back to square one. To me it don't made sense as to why would Subaru make it any different.

Then I found this website; IMPREZA / subaru | model list|JP-CarParts.com.

That website listed S206 models parts, but no R205 models. Still, the S206 downpipe part number is the same as any GRB/GVB model, I then founded out R205 is actually classed as Spec C. And in the turbocharger parts list, there is a special note written in Japanese for R205 and S206 which according to my friend is about annual emission. Ah-Ha~! I thought, maybe what HKS meant to say was their downpipe do not conform with emission for R205 and S206 model.

So I bought the HKS twinscroll downpipe.


Not a true divorced setup. But I like the design as it uses 2 mounting point like OEM and has 2 catalytic converters (which I thought should reduce high pitch exhaust noise).


JDM STI's front 02 sensor is located on the downpipe. I read some run into problem when relocating their 02 sensor from the manifold to the downpipe, but I suggests talk to your tuner and see how they like it to be. My tuner (Delicious Tuning) said having the front 02 sensor relocated to the downpipe is fine. My friend's 2008 STI relocated the front 02 sensor to the downpipe and it runs perfect. The 2015 EJ257 VF37 owner was told to stick the 02 sensor onto the JDM manifold (I am not sure how because that would mean the 02 sensor will take a reading from 1 pipe only, as the JDM twinscroll manifold is a 4-2 design.)


As per HKS instruction, trim the OEM heat shield. The turbo is also wrapped with a turbo blanket. HKS also supplied heat reflective stickers, which I slapped onto the firewall directly facing the downpipe.


And HKS supplied a metal heat shield to cover the catalytic converter facing the CV joint.


Since the R205 uses a Group N 'Red' turbo inlet, I figured I ought to do the same and uses Tomei turbo inlet instead. On VF56, the step-up ring band Tomei provided for VF48/VF49 is not needed. It just fits the VF56 inlet. Subaru mech told me, compared to VF48 the VF56 has larger internal diameter inlet, but I don't know if the outter diameter is the same as VF48. But yeah, it just fits and tight enough for me to lift the turbo by the Tomei inlet without clamping it down.


Installed to stock air box.


Now back to the downpipe. When the downpipe was installed, there was a gap of maybe about 3cm or so. Thankfully, the Corsa catback is a slip fit by design, so I loosened up the slip fit connection before the Y pipe, and slowly tighten the bolt connecting the downpipe and the catback. The HKS donut gasket also won't allow flush joint between downpipe flange and catback flange, but that is fine because it also allows complete seal. There is probably about 3mm gap between the HKS downpipe and the Corsa catback when using the HKS donut gasket.


The fitment is great once the Corsa catback is adjusted. While my finding suggests the GVF and GVB aftermarket catback is the same, I now have some doubt. Yet, maybe my Corsa midpipe was inserted deeper than required when I had the single scroll 3' downpipe (as this is a custom 3' downpipe), because there is still plenty left to go until the midpipe is no longer able to slip into the Y pipe.

Afterall that said and done, the install was problem free.
 

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Discussion Starter #7
So how does the VF56 setup feels like.

Well, since the car isn't tuned for VF56, I thought I will just use Intelligent mode to keep me out of boost. But to my surprise, even on Intelligent mode the car drives soo nice. It actually feels a lot better than Sport mode with single scroll.

It feels like I am driving an N/A car. It felt very natural and responsive. Downshift rev match is so easy even at low speed and what supposed to be 'held back' throttle response mapping. I never use Intelligent setting because it felt so lethargic and I actually think this can't be good for the engine.

Not anymore.

It drives so smooth and easy, it makes me real happy just to drive it home while staying off from boost. I tried Sport mode and the moment I press the throttle on Sport mode, the car is about ready to go. So I just switched it back to Intelligent mode.

Then for the sake of hearing how does it sound if I give it more gas, I roll at around 40km/h on 2nd gear, press the clutch and jabbed the throttle. While I did not saw how quick the rpm rises, my Aquamist flow bar instantly went to max; which means the rpm went up high enough to call for more fuel. Wow, I have never seen my Aquamist flow bar reacting like that before whenever I did that. And the exhaust sounded amazing too!

But of course what I really want to hear is the car going all out, let loose, on full boost!
 

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Awesome post! This is a great example of how good ELH can sound on our cars. With the right exhaust, ELH can sound wayyy better than the UELH rumble. Considering all the positives of running ELH, a tone difference is the only negative, and it your case not at all. Im very curious to see how well the car does on the dyno now that you have gone twin scroll with ELH.
 

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Discussion Starter #9 (Edited)
Awesome post! This is a great example of how good ELH can sound on our cars. With the right exhaust, ELH can sound wayyy better than the UELH rumble. Considering all the positives of running ELH, a tone difference is the only negative, and it your case not at all. Im very curious to see how well the car does on the dyno now that you have gone twin scroll with ELH.
Thanks!

I was quite worried that with ELH the exhaust will sound bad. I am unsure as to what makes mine sounds different to what one would expect when using ELH, bigger downpipe and free flowing exhaust. I mean, it is not an apple to apple comparison because it is an oem twinscroll setup and using a bigger downpipe but with 2 catalytic converters.

The oem manifold is actually impressive to look at. It is encased inside the heatshield and unlike the single scroll heatshield they weld shut the twinscroll manifold heatshield. It looks as if Subaru really put much care to it. And of course the heatshield would trap the heat so the manifold dont lose the heat for fast response.



My reason of using oem manifold is because I do not like the idea of having to wrap Tomei twinscroll manifold. I could get it ceramic coated, sure, but the one other thing which made not getting the Tomei twinscroll manifold is because their twinscroll manifold is made for bigger than oem turbo. Since my primary requirement is engine response rather than outright power, I decided it is best I go with the oem twinscroll manifold.

Some may not see the point of going through all the trouble and cost of doing this conversion; and they do have a point. If what you want is power at high rpm then this is not something you want to do. A road course car is probably best to go with something like Fullrace stock location turbo.

I don't know the exact power my friend's 2008 STI VF42 made, but I will say it is a lot quicker than a single scroll stage 2. It isn't even a fair comparison to be honest. It is very, very quick.

If I have to guess, the most it can make is probably 350bhp (or, engine horsepower). Yet peak hp is only half of the picture, because the way it gets to the peak hp is what is more important for me; broad torque from anywhere in the rpm that is suited in real world driving. This makes it possible to use most of the power for most of the time.
 

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Discussion Starter #12
Well, the tune is going well but is not completed yet. Still, here is a video of maybe between 30% to 50% throttle pedal.

 

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Discussion Starter #13 (Edited)
Well, it looks like at this point the tune will continue after the 2nd of Jan 2018.

Yet because the tune is about 80 to 90 percent completed, I can drive the car around and enjoy some of its power. Is also a good time to try out what it is like to drive outside full throttle. Afterall, this is one of the reasons of why I choose to go for this setup.

But to get it out of the way, the acceleration feels very strong during log pull where full throttle is required.

And little bit more about the Corsa with this setup:

Sound wise there is no problem with droning and/or excessive loudness. And is not that I am being subjective; because there really was none of those problems. The VF56 twin-scroll definitely made the exhaust sounds different to other Corsa with single scroll on ELH header. No I do not think it sounded like a Porsche, but it does sound like a highly tuned engine that's smooth and free revving; especially @ 7,300rpm. It is never ear piercing, and good balance of tone throughout the RPM.


Now to the driving part.


If you are the kind of person who thinks the STI suffers from turbo lag (not turbo threshold), and you wish there is more power below 3000rpm; then this is the turbo for you for as long as you are satisfied with stage 2 peak power level. Yet, I felt a slight improvement at the top end with setup vs the single scroll.

This setup makes the STI very flexible because there is power everywhere. The maximum boost is still at around 3800rpm to 4000rpm, but you won't feel like it is at 4000rpm because getting to the maximum boost is done with linear fashion - and very quick. The spool is pretty much instant. The car feels like it has lost a lot of weight.

Driving around town takes some getting used to because now the car is very responsive. But it isn't jerky or anything like that. Is just that coming from single scroll to this twin scroll setup requires right foot calibration.

Cruising on the highway with 6th gear around 65mph on the tacho, the engine no longer feels lethargic. If I want to leisurely overtake the car ahead of me, I can just press the throttle and the car will just respond and go. And if I am in a bit of a hurry, just use 5th gear. And it is enough just to use about 30% throttle; on Sport mode.

Handling is also a lot easier thanks to its linear and broad power band. A corner that used to require 3rd gear can now be taken using 4th. Mind you, this is not race driving. Just taking a corner nice and swift. This turbo, together with my suspension setup made my STI feels so friendly because of its flexible nature.

It also feels like how a modern turbocharge car should be. A car in this segment that feels like this is BMW with N55 engine. The N55 engine feels like the turbo is assisting the engine, and not the other way around. It is a lovely engine, and yeap it uses a twin-scroll turbo. A VW Golf R on the other hand shows a promising power band. On paper it is said to make 280ft/lb as low as 1,800rpm, but I am not sure why the powerband feels worse than a stock STI. Maybe it is to do with it using a single scroll turbo. Clearly there is a massive difference of throttle response between the BMW and the Golf R, despite it on paper both offers similar table flat torque curve from around 1500rpm to 5000rpm.

But I also have a VW Golf MK6, yet mine is equipped with 1.4L twincharger engine.

The VW 1.4 twincharge engine uses supercharger below 3000rpm, and the turbo takes over above 3000rpm. While not powerful (about 200bhp max with Revo Stage 1 tune), the accessibility to its power across wide range of RPM and combined with 7 speed DSG made the car very fun to drive. Unless it is on a long stretch of road, I have all the confidence to leave a stage 2 STI behind in a fast pace zig-zag contest through traffic with this rather unassuming car. But now my STI feels as agile as my Golf, and that made me feels very happy.

The part that I do not understand is, why can't Subaru just sell the 2.5L STI with a twin-scroll turbo. Such a miss opportunity.
 

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Discussion Starter #14
So i received an email from Delicious Tuning and looks like the tuning is done. Yay!!

Well at least now everything is ok as Delicious Tuning already confirmed the tune is done. And I did not run into any hiccup during the entire conversion and tuning process. Everything went as smooth as it can be. Prior to the tuning i made sure the engine compression is perfect, and replace with new engine oil, new spark plugs and new air filter.

I will do full throttle video and lets hear this Corsa at full throttle run.

A little bit more information about this turbo based on what I saw on the datalog.

I saw on the log when the wastegate duty cycle was set to constant 67.5%, on third gear the turbo boosted to 23psi. No knock correction or knock retard were registered during that pull. Since the aim was 18psi to 20psi, the wastegate duty cycle is now set to 50% and it settles at 20.44psi. From thereon the wastegate duty cycle is increased to 80%. The boost a 7000rpm is 14.5psi, then dies down afterwards with rpm limter set at 7,300rpm or so.

Based on the time log by ecutek in second, from 2000rpm to 6500rom using third gear; running on 20.44psi is quicker by 1.16 seconds vs the single scroll setup (at 19.76psi). At 23psi and constant 67.5% wastegate duty cycle, it is 1.97 seconds quicker vs the single scroll. It could be a full 2 seconds quicker if the wastegate duty cycle is increased to 80% at the top end.

While there were no knock correction at 23psi max boost, I am not sure if that is ok on the long run for both the turbo and the engine. I am not gonna lie, if possible I want to boost to 23psi than the current 20.44psi because it feels a lot faster during that one and only log pull at 23psi boost.

But then again I am not sure if more boost at the midrange has any benefit because in real world I don't do a pull from 2000rpm. And as it is now is already super quick for an STi from low end to midrange.

So I think for the sake of safety it is wise to leave the max boost as it is. Unless Delicious Tuning said is ok.

Am I happy with the result of this conversion? Well yes I am very happy. If I can meet one of the engineers in Subaru I would beg them to please just add twin scroll to the EJ257 as it completely improve the dynamic of the car and benefits most buyers.

But they already knew this anyway.
 

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Discussion Starter #15
So I just came back from a bit of hooning, and I managed to get some video recording.

Sport sharp.

Sorry for the bad night image quality. It is GoPro afterall.

And below is a single scroll video recording
 

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Discussion Starter #16
More driving update


After more driving and getting used to the powerband, I now use Intelligent mode as my daily driving mode. It is very nice and it is definitely a lot quicker than VF48 on Sport Mode. Finally this mode makes a lot of sense for daily driving.

Sport mode, is very nice for highway use. I can use it for daily driving, but if there is bumper to bumper traffic I keep finding myself pressing too much throttle. Sport mode feels slightly quicker than VF48 on Sport Sharp - but with throttle response immediacy that VF48 cannot hope to match.

Sport Sharp mode is of course the racing mode. I only use this mode where there is a lot of incoming cool air - such as on the highway or on the track. In this mode the car becomes very urgent. While there is a lot of bottom and midrange grunt, I still drive it as if it is a VTEC engine (I believe all car should be driven in such manner) when full throttle is required, and the engine revs freely to 7,000RPM (cut off is set at 7,300RPM).

Gone is the horrible turbo lag between gear changes, and this is one of the reasons of why it is a lot quicker than VF48 could ever be. With VF48, Sport Sharp feels fast during in-gear acceleration, but during up-shift there is turbo lag that delays the next round of acceleration. Not only VF56 is a lot quicker during in-gear acceleration, it also allows immediate response during up-shift. And this is especially useful to me because I do not use advance feature such as flat foot shifting.

So now my STI's power feels balance from bottom to the top, which makes the power delivery feels smooth and linear. Kinda like having a V8. Peak power is most likely the same as any other stage 2, maybe a little bit better and I am guessing no more than 350BHP, but it is the accessibility of the torque and its immediacy from anywhere in the RPM range that makes the big difference.

And I guess that concludes this project!
 

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Discussion Starter #17
It has been a long time since I posted something.

Anyway here is a video of the Corsa with my JDM twin-scroll setup.

Recorded using Sony action cam without external mic.

 

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This sounds like an excellent setup, thanks for all the details you have included! I'm very tempted to try it, but it sounds like obtaining a VF56 could be tricky.

I'm very interested to know whether you made any fueling system modifications, and whether you experience the "stumble" with your setup?
 

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Discussion Starter #19
This sounds like an excellent setup, thanks for all the details you have included! I'm very tempted to try it, but it sounds like obtaining a VF56 could be tricky.

I'm very interested to know whether you made any fueling system modifications, and whether you experience the "stumble" with your setup?
Hello,

Yes is an excellent setup for broad power and better top end vs the VF48.

I don't have any fuel modifications and no stumbling either.
 

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This sounds like an excellent setup, thanks for all the details you have included! I'm very tempted to try it, but it sounds like obtaining a VF56 could be tricky.
I haven't had any luck sourcing a VF56, but I was able to find a VF58 (ST14411ZR010) for the low price of $3,380 plus shipping.. I believe that this was the turbo used on the S206 & S206 NBR.

ST14411ZR010 / TURBO CHARGER ASSEMBLY / IMPREZA / subaru | part detail|JP-CarParts.com

I like the OEM/JDM rareness factor, but for that price I'd just go with something like the Blouch Dom 1.5XT-R twin scroll turbo with the JDM manifold and downpipe. It's a little bit larger of a turbo, but is half the price.

dlheman - very nice setup! Thanks for sharing all of the details. Any recommendations on where to source rare JDM turbos like yours? I'd love to do something like this to my '19 STI once it's paid off and out of warranty... but if I'm being honest, I probably wont wait that long :lol:
 
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