To Twin-Scroll or not to Twin-Scroll, that is our Question of the Week
In the Subaru community, the Twin-Scroll turbo configuration that was used on the JDM STI starting with the Version 8 STI is considered the ideal turbo setup.
There are a couple of reasons for this.
The main one is that a twin-scroll turbo uses an equal length manifold, and it splits the exhaust pulses up into 2 completely separate sets of pipes all the way into the turbo. This allows for the optimal pairing of exhaust pulses to in theory maximize the spool characteristics of the turbo.
The equal length manifold also performs better in high rpm ranges, so the twin-scroll turbo should have better top-end performance than a comparable single-scroll turbo.
On paper everything points to why a Twin-Scroll turbo will perform better. So when we set out to build our Pikes Peak race car back in 2013 and 2014, that is the path that we decided to go down.
So what is involved in a Twin-Scroll Turbo Conversion?
And is a Twin-Scroll turbo really that much better than a comparable Single-Scroll turbo?
To answer this question of the week, we went back and looked at all of our results with the various twin-scroll turbos that we have tried on our Pikes Peak Race Car and did our best to put all of that information together here.
If you want to take a closer look at any of the dyno sheets, follow the link below to our blog post on our web-site:
www.flatironstuning.com/blog/...
Thanks for watching and if you have any questions you would like us to answer, please leave them in the comments below.
Stay Tuned!
In this video:
00:00 - Intro to the Question of the Week
00:23 - What is a twin-scroll turbo?
01:24 - What is involved to convert to a twin-scroll turbo?
02:50 - Is it worth it to convert to a Twin-Scroll turbo?
04:44 - Our results with Twin-Scroll turbos on our Pikes Peak WRX
06:32 - Our results converting our Twin-Scroll turbo to a Single Scroll
My experience: Now granted I had access to all the parts and tuning was easy, that part can be a hassle and very expensive. Mid Ohio I ran a better time with a single scroll(equal length header) than my twin scroll on the same engine(2L 9.7:1 compression), but I did better at my local Auto and Rally X events with the twin scroll. I'd say for the most part it should be application based and whether or not you really "NEED" a twin scroll. 2L daily, yes I actually saw better mpg(+4-5mpg) with a twin scroll, but if you plan on using the car for what you actually bought it for(let be real folks you didn't buy it to drive to and from work) then a single scroll would be better. Again guys thanks for the great content and I look forward to seeing more. Hope you'll be at PRI this year.
Exactly... For max power application like drag strip.. definately single opens up more power level option... But for rally,autoX,gymkhana and such technical circuit layout, definately twinscroll have wayyyy better driveability and more responsive
Thanks for all those details Keith. Nigel has mentioned some of your results with the twin-scroll turbos, and at some point, it would be a fun conversation to have. I'd love to get more details. Thanks Keith. Stay Tuned!
Thank you guys for no BS technical content. I can't tell you how many things I've learned & how many times I've changed a future plan for a build due to your videos! If you guys are ever in Oregon hit me up I'll buy you a beer 🍻!
That is awesome to hear! Thanks Ben! Very glad that we could help, and there is a lot more in the works. Stay Tuned!
Thank you for sharing this information! Very informative and helpful.
This is super informative. Thanks for sharing your twin scroll experience.
Absolutely! Glad we could help and Stay Tuned!
Love the vids as usual, being in the market for an ej207 for my 05 wrx, has always made me question whether I'd want a twinscroll turbo or not, kinda helps me avoid the hassle of choosing the right turbo and sourcing a downpipe. Keep up the great work!
Very glad we could help! Keep in mind that the Twin-Scroll results on the EJ207 may be a bit different. All we can do is post the results that we have. And definitely watch out for the EJ20X and EJ20Y engines as well. Thanks for watching and Stay Tuned!
The advantage of the twinscroll is really that last 10% efficiency kinda deal. I’ve driven two JDM Legacy 2.0s (I built both of them) with the same engine, one with a td05 18g twin scroll and another with a vf34 with the same supporting mods. The vf34 comes on boost more violently and feels faster in the mid rage due to the aggressive transition. The twin scroll was much better off boost and had a linear and progressive power curve. Top end was very similar. Fuel economy on the twin scroll is slightly better. I currently have a twin scroll 1.5xtr on a JDM LGT with a EJ207 and built dual avcs heads, that turbo is perfect on that combo and makes 410whp on e85 at 24psi from 4K-8k (this is Australian hp so like 600hp US)
Thanks for all that information! I think that the Twin-Scroll turbos definitely work better on engines that are set up to rev a bit higher than the standard EJ25. You get to spend more time where that turbo excels. Thanks for watching and Stay Tuned!
I've been waiting for almost 5 years for a video on this topic and question!
Very glad that you found the video! Thanks for watching and Stay Tuned!
This is why I love Flatirons. You guys are badass and amazing at spreading proper knowledge. ❤️ Grassroots Rallycrosser and Subaru Dealer Technician approved!
Thanks very much! Really appreciate that, and we always do the best we can. Thanks for watching and Stay Tuned!
Grazie dei vostri preziosi consigli
Absolutely! Thanks for watching and Stay Tuned!
Love this kind of content 👍🏽
Thanks very much Jairo! Stay Tuned!
I think on a boxer engine with long exhaust headers twin scroll is less beneficial. Something people do not take into account is the increased surface area of the exhaust walls, that being if you run two pipes equal sectional area as one pipe. When you look at aircraft surface area, even if aerodynamic the more area the more drag you have causing turbulence and resistance/pressure. On a short run exhaust manifold, especially where they are not equal length, a twin scroll setup is more advantageous. Having small exhaust volume between exhaust port and turbine inlet allows for higher pressure spikes from interfering exhaust pulses. Having a larger volume but also twin scroll you are introducing more friction. The same can be said about bends or even with a water pipe, the longer the pipe the more pressure loss you get. running one water hose of a specified volume will have less pressure drop than two of equal volume. I am building a Turbo helicopter engine and a twinscroll is better as it is a short header (lighter), it reduces backpressure and egts, but I can also merge the collectors into one scroll for high altitude response.
Thanks for the comment. There is definitely more going on with a twin-scroll turbo than you would usually assume. Thanks for watching and Stay Tuned!
Yep, that's exactly what I was thinking. I feel like you might be able to get away with the same runner path if the runner diameter were small enough to allow the exhaust pulses to reach the turbine with enough energy to take advantage of the twin scroll snail, but I'm just guessing. I'd really like to see what numbers we'd get from that manifold if we were to use Graham Bell's equation though, just out of curiosity.
Great video! One thing I think its important to make a note of is that you're likely seeing some of these issues because you are staying on the OEM TS style flange and housing. A proper twin scroll setup by someone like full race with a B2 BW housing produces all of the good with none of the bad of the twin scroll setups. Yeah you need their header and up pipe, etc. But you need all of those for a TS install anyway... Might as well just run a BW EFR :D
Thanks for the comment. When you get into big turbos, the twin-scroll option can still be a bit complicated. How the engine is built to make power is a big piece of the puzzle for that decision as well. It is beyond what we have played with, so I can't speak to it with the kind of data that we have for the stock-location turbos. Someday maybe that will change :-) Thanks for watching and Stay Tuned!
Very helpful when you go over specific turbo models! I wonder how the Garret turbos compare. Ive seen a few 3071r ej207s
Thanks for your question. Yes, the Turbo Dynamics MDX555-450/LM450 is based on the Garrett GT3071 actually. I'm sure that Turbo Dynamics has some data about those turbos on EJ207 STI's. Thanks for watching and Stay Tuned!
I'm running a 1.5XTR T/S and its incredible, previously used a 2.5XTR which was exciting but less driveable, narrower power band, and ultimately less power at redline due to inefficiency in the hot side 8cm probably. Mustang dyno tuned350 whp 380tq, 28psi, ID1000, Fuelab FPR, APS TMIC, 93oct stock EJ257 engine with JE pistons stock bore and CR. Responsive autocross build. Yes you can achieve this power without twin scroll, its not about that, its the delivery of it.
Glad I saw this video, I’ve got the dom 5 and if I would go bigger I was going to switch to twin scroll because I didn’t want more lag than I already have but if larger twin scroll turbos don’t spool like I thought then there’s no point for me to do all that.
Glad that the video was helpful. I would definitely recommend trying to take a look at a dyno sheet of any large turbo you are considering (twin or single scroll) ideally with a similar build to what you have. That is the best way to get a sense if the useable power will be where you want it. Thanks for watching and Stay Tuned!
Hey guys great content! Do you guys happen to know if the tomei expreme ti header and up pipe will work with a TSR 70 twin scroll turbo? Or is there a suitable alternative? Thanks in advance.
battled between single and twinscroll when deciding to run my 6758 EFR. due to simplicity and marginal gains with TS on this size of turbo i stuck with single scroll. Would you agree the EFR's are a bit of a caveat when it comes to TS performance on a subaru? having driven a TS EFR8474 1.05A/R back to back with my older GTX3076 Tial .82A/R (08 STI and 05 STI), the response and spool up of the EFR was better than my smaller Garrett. not to mention it made a good 100whp more on 30 psi than my did but thats a seperate discussion. Thanks for continuing with the podcasts and informative short tech videos!
Thanks for your question Dillon. When you get past stock location turbos and into rotated Garrett turbos, etc., things get even more complicated. There are a lot of aspects of a build that can add up to the point where a twin-scroll, or single scroll turbo would deliver better results. Things like engine rpm range, cams, valves, headwork, size of exhaust manifold, use of the car, desired rpm range of powerband, etc., all have to be considered and weighed. It gets more complicated fast :-) We may be working on some more content in the realm of this topic... Thanks for listening and Stay Tuned!
Finally you guys squashed this myth! Thank you for the graphs with proper comparisons
Thanks for watching, and glad that the video was helpful! Stay Tuned!
In summary, putting aside bogwarner efr or lm450 s60 being the best ts turbo, some of the said benefits going back to single scroll on the lm450 in your back test maybe largely due to unequal length header. And accordingly to ur findings one should get ur engine higher reviving and have broader high rpm power brand to make use of better response getting on the throttle on high rpm with ts setup. That means if one is already with a ts setup (for jdm spec c folks like me), don’t panic jumping into single scroll just keep the setup. As for those currently with single scroll don’t try too hard going thru all the hassle jumping into ts, unless you are making sure you need the upper end rpm benefits getting back on the throttle on this range (but that may mean that you need upgrades to head work and etc to make power on higher rpm range). I guess that’s what you try to say here.
For stock block 2020 STI which turbo would you recommend not looking for big numbers just want good spool for auto x and time attack track day car. So happy you made this video it saved me a lot of time and money 😂
16G or 18G. Blouch and FP seem to be the most popular
Thanks for your question. If you just want a small change, the VF48 HF could be a good option. It would let you get close to 300 whp on pump gas, and close to 350 whp on E85. www.flatironstuning.com/ihi-vf48-hi-flow I will say that they aren't currently available though. I'd definitely recommend looking at our blog about picking a turbo here: www.flatironstuning.com/blog/how-to-pick-a-new-turbo And I'd say look at the Turbo Dynamics MDX555-400. We really like that turbo for a good power band and response. It can get into the low to mid 300's on pump gas, and close to 400 whp on E85. kzhead.info/sun/lNKjp5SLrmhrZXk/bejne.html Hope that helps and Stay Tuned!
Nice! Was this recommendation for the EJ series Turbo upgrade? I'm asking because I went EFR 7163 twinscroll for a FA20 build. The idea was response, and to have the top end not choke out. I have a question, how would you begin to tune your suspension? Does it depend on the track? Do tires play a huge role?
Thanks for the comment! Yes, this video is all about the EJ series of engines. The FA20DIT puts the turbo so much closer to the engine, there are many more benefits for the twin-scroll turbos on that engine. Which is why it comes with that turbo from the factory most likely :-) Suspension set-up is a big one. We have had a number of questions about that, and it is something that we are working on tackling. But yes, tires are a huge part. And alignment. And just about everything else. Thanks for watching and Stay Tuned!
@@FlatironsTuning thanks for the response. I assumed that the FA20 and the Fa20 DIT would both benefit from a smaller twin scroll. At least when it comes to response. I appreciate this series of videos it provides a lot of information and gives some experience along with it.
Would the results be different with the 207?
On your back to back Dyno graph of the twin scroll versus single scroll it also shows you guys changed fuel, from 104 to E85. Did you guys do any Dyno pulls on the single scroll on 104 before switching to E85?
Thanks for your question Ross. We did not unfortunately. When we made that switch, there was a lot of other changes that happened to the car at the same time. Bigger injectors was one, but we also had to change out the bladder in our Fuel cell for a new one to handle E85. So it just wasn't possible to see what the car did on Race gas before putting in E85. Thanks for watching and Stay Tuned!
I’m wondering if the extra exhaust flow from the e85 having to run richer actually helped spool the turbo quicker…
@@zokusharuuku1091 E85 does generally help to get a turbo spooling up a bit more quickly. It also does really well with timing, so that can be part of the equation as well. Thanks for watching and Stay Tuned!
was actually considering twin scroll as a street setup, but i think ill stick with the standard scroll..thanks
Thanks for watching and glad that the video helped! Stay Tuned!
Do it!!! Just got my vf37 twin scroll tuned. Made 380hp full boost at 3200 rpm. Such a fun way this car pulls. So linear and quick
Wrote that before watching the video. What dyno got your 350 hp value? Cause that turbo is massive compared to mine and I got 325 on 91 and 380 peak on e91 makes 21 lbs of boost that holds till 7k. Is that altitude difference or maybe inaccurate dyno
Thanks for your question. We compiled data from our tuned who has used 2 different dynos. The first few were on a Dyno Dynamics, and the last 2 were done on a Mainline dyno (similar to, but more advanced than the Dyno Dynamics). Both are Eddy current dynos. Thanks for watching and Stay Tuned!
This is a good video. On the newer 15+ FA20DIT, the true equal length header with a twin scroll turbo is how that engine was designed; therefore, I would assume a guy would want to keep the twin scroll configuration on this engine. What do you think?
Thanks for your question. Yes, the placement of the turbo is a big part of it as well. The closer that you can get the turbo to the cylinder head, the better the Twin-Scroll turbo will work. That is why stock for stock, the FA20DIT WRX has more tuning potential right out of the box compared to the 15-21 STI that is using older design EJ engine and turbo configuration. In short, no, you wouldn't want to change away from the twin-scroll turbo on your FA20DIT WRX. For that engine on that platform, it works very well. Thanks for watching and Stay Tuned!
@@FlatironsTuning thank you for your reply. I am currently in the middle of a pretty big makeover, and I am working on mounting a G30-770 turbo with T4 divided twin scroll turbine housing to the odd shaped flange on the header. Not easy to do properly but will be well worth it!
@@2018wrxaddict Wow, that sounds like a really cool project! I am sure that if/when the STI gets an FA24DIT engine, the turbo set-up should be the same as what you are using on the FA20DIT. And once that happens, I think that there will be a lot more energy put into big turbo options for that front-mounted twin-scroll turbo. Good luck with the project, and let us know how it turns out!
@@FlatironsTuning I'll definitely update you!
Try gtpumps(Australian company) for a twin scroll. My Liberty , aka Legacy gt (5th gen low mount turbo using a turbo for the FA20) achieved 27 psi at 3200 rpm (ej255). It's a very different performance characteristic to other Subaru's I've driven (owned a my02 STi and driven a 2014 WRX)
Thanks for the suggestion and thanks for watching. Stay Tuned!
What size of tires and wheels are you guys using on your hill climb 2014 WRX? Thanks!
Thanks for your question. We were running 17 x 9 wheels and 255 width tires previously, but for the last 2 years, we have moved to 18 x 9.5 wheels and 245/40-18's which are more like 275's. Thanks for watching and Stay Tuned!
I have a question. Subaru wrx sti 2019 At the moment my built motor has a gt pumps s03.5 Making around 406whp I'm not impressed with it, comes on to slow for me. Car has a ams manifold. I'm thinking about the blouch 3.5 twin scroll turbo. Wouldn't this come on a lot faster?
I'd say that is unlikely based on our experience. For more specifics on the Twin Scroll turbos we have worked with, take a look at this video: kzhead.info/sun/lpGTlrSjbmeKnZ8/bejne.html&feature=shares Thanks for watching and Stay Tuned!
The better question would be: what is a good replacement for the IHI VF37? if you can't manage 2,4k 😐
I’m surprised with the results. Cool
Thanks for the comment! Honestly, we were surprised more than once in this whole process. But in the end, it did help us to get where we are. Thanks for watching and Stay Tuned!
All Taiwanese manufacturers cancelled the production of their twin scroll 0.73 a/r Td05s (MAMBA, Kinugawa) and twin entry single scroll 0.57 a/r (Arashi) turbine housing for a twin entry but single scroll 0.73 a/r turbine housing. Do you have any idea how they perform? Was this change a good idea? Do you know anything about this?
Thanks for your question. Unfortunately I don't have any information about those turbos. Thanks for watching and Stay Tuned!
@@FlatironsTuning my opinion is that this change is for the worse, but I don't have any data about this, so please if you know anything, I am very curious to know!
i got a 2010 hatch with ej20x. i picked up tomei ts headers and dp. thinkin about a vf38. would i have reliability issues with this set up? i picked ts because of the timing thing with the swap.
There is 2 different flange styles for twinscroll EJ turbos. The VF36/37 style is what came on STI's in japan. The TD04/VF38 style came on Legacy GT's. The flanges don't match the STI, and the Legacy GT twinscroll exhaust manifold has smaller pipes. AND there is very little in the way of upgrades for that style turbo. Best bet is to get a VF36 or VF37 STI turbo, buy the tomei STI TS headers and enjoy your improved response.
I find the JDM twin scrolls are much more responsive and have a wider power band than the single scrolls … and while tuning I realized why subaru did it .. just looking at the data , I tend to run lower wastegate duties than the single scrolls to meet and maintain my boost targets. That’s just my experience
Thanks for the comment, and thanks for watching. Stay Tuned!
Twin scoll👍 I'm biased as I have an FA20DIT
Definitely works well there :-) Thanks for watching and Stay Tuned!
I am putting a gtx3076 0.82A/R on my stock 1jz gte non vvti, but I cant decide between single scroll or twin scroll. If someone could recommend which set up to go with that would be amazing, I will be using a Pulsar turbo and 6boost manifold. Thanks
Thanks for the question. I'd say that the closer you can get the turbo to the cylinder head, the better your results will be if you go twin-scroll. Also, since that is a 6 cylinder engine, it may actually be easier to build a twin-scroll manifold compared to a 6 into 1 manifold. Sounds like a fun project! Thanks for watching and Stay Tuned!
Twinscroll setup downpipe collecteur and turbo and k&n air filter should work fine and mapping ecu
This isn't my experience at all. Usually you see at least 10% improved top end and improved spool by about 400rpm. The turbo efficiency band is greatly inproved as well. I'm thinking there was probably something wrong or unoptimized with your exhaust configuration. Unless you want to do something cheaper its almost always better to do a twinscroll turbo.
Thanks for your comment. Honestly, we didn't expect the results that we found either. That is why we tried this many turbos, etc. We just wanted to put together the data that we had and share what we found. Thanks for watching and Stay Tuned!
and did you test 100% back to back with the exact same turbo ?
@@blow0meso I have experience switching from a twinscoll to basically a single scroll just by making the header unequal length. Changing nothing else on the exhaust or turbo. Performance is lost across the board including spool. In their example I feel like there is too many variables changed. Yes it might not make a difference but if it's done properly you should always get more performance. The turbo also has to be designed from the ground up to be twin scrolls. Just swapping a housing on the turbo doesn't make it a proper twin scroll. My baby sized Garrett MGT2259S was making much better numbers then most of their twinscoll turbos with much less spool time.
how was is fitting up the dry sump?
It wasn't too bad, but definitely involved. Take a look at this video: kzhead.info/sun/ZdaOkp2xpn6NlIE/bejne.html And this video: kzhead.info/sun/mNqMnpZrm3Zpa40/bejne.html Hope that helps and Stay Tuned!
The JDM guys rave about the throttle response and power from 2000 to 8000 on the ej207. If you want a 350whp can carver with response and a broad power band would it make sense then? Cost aside
Is there a benefit going TwinScroll on the EJ207 ??
On the EJ207, if you are revving higher, there may be more of a benefit in the upper rpm range with the Twin-Scroll turbos. It is definitely happier the faster the engine is spinning. But picking the right Twin-Scroll turbo will still be a big key to success there as well. Thanks for watching and Stay Tuned!
@@G1itzik Thanks for your question. As with our experience, I'd say it would be best to get as much information as you can so that you can compare your pick of a single-scroll turbo to the twin-scroll turbo you are considering. Make sure that the powerband is where you want it to be. Thanks for watching and Stay Tuned!
@@FlatironsTuning The twinscrool is much more better in 2.0 subarus, in usdm 2.5 liter due to displacement the turbo will spool faster and you could use a bigger turbo to have the powe band on reasonable level, especially with equal lenght headers. I would say twinscroll conversion is worth only on 2.0 motors, if you could afford the full swap (head, manifold, pan, turbo and downpipe), in 2.5 it's better to buy equal lenght headers with ball bearing turbo.
@@jakubclash7629 Thanks for the comment. We do wonder if it would work better on a high revving 2.5 liter engine, but that is a little less common, and we haven't had the chance to do any testing with that set-up. Thanks for watching and Stay Tuned!
So is a twin scroll just a better setup for the EJ207 engines rather than the EJ257s?
Thanks for the question. It seems from the feedback here that a lot of people with EJ207 Twin-Scroll setups prefer them. And given the nature of the EJ207, specifically the fact that it rev's higher, and doesn't make as much low-end torque compared to the EJ257, the Twin-Scroll turbo may well be a better fit there. Thanks for watching and Stay Tuned!
@@FlatironsTuning the factory ihi twin scroll turbos were only really meant for the ej20s (205/7/x/y) imho the vf36 is the best same as the vf37 but with a titanium wheel for faster spooling which came stock on the v8/v9 sti spec c jdm models. and can make good power for a street/track car. but for big power on a built engine a big after market single type will give you better results.. but a good tune can make or break a ej engine no mater what which setup you prefer. G.. NZ
@@gregm7231 Thanks for the comment Greg. Stay Tuned!
I wonder how much difference the JDM 6mt makes. I’ve got an ej207 and the JDM 6mt and it spools significantly earlier than my ej205 and with the gearing in that 6mt it feels like it’s almost always a fraction of a second from being on boost. Now the tickling 3k rpm’s at 65mph doesn’t make it the most enjoyable freeway cruiser, but give it some twisty roads and it starts to shine.
Honestly twin scroll is pretty difficult from finding parts for it and even replacing parts is hard there is just a handful of turbo's out there and each one will need to be tuned. I currently run a vf37 and I can't find a decent replacement because I wont spend 900 on a unit that I can tell is in worse shape then mine. So if anyone has a decent example they want to sell let me know
From personal experience with several Twin scroll or twin entry turbo on JDM Subaru Impreza STi ,I would probably choose billet upgrade of VF37, it probably will be cheapest upgrade and how much it will make? 380-400bhp at flywheel You have right now several options like MDX555 from Turbo Dynamics, LM4xx series from Litchfield or MDX321 series from Lateral Performance or Chevron motorsport Twin scroll/Twin entry turbo which is based on HTA turbo and then you have choice of Mamba gtx3076r twin entry or Arashi twin entry gtx3076r or Blouch Dominator series We have run or tried on our JDM Subaru Impreza STi Hawkeye Chevron motorsport 73HTA twin entry and that turbo is awesome, makes 465bhp at 99 RON and with 20% of methanol it making 500bhp or close to that figure, right now we are switching to MDX321V with Twin entry housing and hopefully it will make easier 500bhp We have tried as well Mamba gtx3076r twin scroll turbo which was making 430bhp at 1.45bar boost and we have tried too Arashi twin entry gtx3076r turbo too which was making 440bhp at 1.5 bar, it would probably make more MDX321 series is proven for me, previously we have run MDX321T and that turbo was making 490bhp and LM4xx series too is proven on twin scroll and Chevron motorsport twin scroll turbo too are great turbo although they are kinda expensive With any of them you will need to have car mapped or tuned that's for sure
You chose the wrong company to use for your twin scroll turbo. BorgWarner EFR is the best Twin Scroll. Try that before saying it’s not worth it.
Thanks for your comment and Stay Tuned!
Would a twin scroll be better than single for inlet restrictor situations?
Thanks for your question. It would actually be worse. Because twin-scroll turbos (in this configuration) spool up a bit later, you would be limiting your power band even more to switch to a twin-scroll turbo if you had to run an inlet restrictor. Thanks for watching and Stay Tuned!