dahoseman Posted February 3, 2015 Share Posted February 3, 2015 This is a bit of a loaded question. All other things being equal, how big is the difference (feel, power, spool) between single scroll and twin scroll versions of the same turbo on the same setup? I am considering buying an older STi as a play toy AND DD. I had been planning on this for quite some time and was planning on building the power train around a twin scroll turbo, likely Dom 1.5XTR. I have collected headers, down pipe, gaskets, flanges, and various other parts in anticipation of going with a twin scroll setup. It turns out that the car I'm looking at already has a Dom 1.5XTR installed, but the single scroll. I don't have any personal experience with twin scroll arrangements, but I my primary goal is developing power as low as possible and up through the RPM band. I'm torn between between leaving the turbo setup as-is (because it's already there), or installing the twin scroll parts I've collected along with a twin scroll 1.5XTR and selling the current single scroll setup. Any info or personal experience with either? Link to comment Share on other sites More sharing options...
Underdog Posted February 3, 2015 Share Posted February 3, 2015 Speaking from the experience of going with two separate twinscroll setups (the latter being the TS 1.5XTR) I would say don't bother. If you were starting from scratch it might (MIGHT) be worth the added expense and lack of commonly available parts and gaskets, but otherwise it is not worth the hassle IMO. The Crimson Dynamo Link to comment Share on other sites More sharing options...
dahoseman Posted February 3, 2015 Author Share Posted February 3, 2015 Speaking from the experience of going with two separate twinscroll setups (the latter being the TS 1.5XTR) I would say don't bother. If you were starting from scratch it might (MIGHT) be worth the added expense and lack of commonly available parts and gaskets, but otherwise it is not worth the hassle IMO. Well, I already have a full set of gaskets, JDM headers, the down pipe, and all flanges ready to install. I even have the VF36 BB turbo that came with it, though I was planning on something with slightly higher flow. If I don't install them, I suppose I will sell them. I was just curious if there was any real-world appreciable difference? If there were two identical cars, the only difference being that one has the SS and the other the TS version of 1.5XTR, could a driver tell the difference between them? Link to comment Share on other sites More sharing options...
dahoseman Posted February 3, 2015 Author Share Posted February 3, 2015 still interested in TS experience Link to comment Share on other sites More sharing options...
Underdog Posted February 4, 2015 Share Posted February 4, 2015 I think you will be hard pressed to find the A-B comparison you are looking for. Having driven my td04hla-19t against smaller stock-sized turbos and the difference in response is evident. I recently did a single scroll 1.5xtr on a customers '12 WRX which I can compare to my TS 1.5xtr (once complete) but even then you have the difference from his D25 heads with stock cams and my PnP B25 heads with Tomei Poncams. The Crimson Dynamo Link to comment Share on other sites More sharing options...
dahoseman Posted February 4, 2015 Author Share Posted February 4, 2015 Well, i wasn't necessarily expecting a direct A-B comparison (though that would be awesome). I was just hoping someone had enough experience with TS and SS variants to give some personal experience for my data gathering. Link to comment Share on other sites More sharing options...
dahoseman Posted February 5, 2015 Author Share Posted February 5, 2015 I think you will be hard pressed to find the A-B comparison you are looking for. Having driven my td04hla-19t against smaller stock-sized turbos and the difference in response is evident. I recently did a single scroll 1.5xtr on a customers '12 WRX which I can compare to my TS 1.5xtr (once complete) but even then you have the difference from his D25 heads with stock cams and my PnP B25 heads with Tomei Poncams. Maybe I should find a TS and convince someone to let me borrow it. Given that I really like a wide torque band with early spool, and I have essentially all of the TS parts sitting in a storage unit, would you recommend swapping out the single scroll for the twin scroll? Have you found TS to be a little more 'driveable' in city traffic? I also don't have any experience with PnP'd B25 heads, other than reading a few things on this forum every so often. I see that you're in the middle of your build/installation, but have you found the difference to be worth the effort for those heads? Link to comment Share on other sites More sharing options...
lingling1337 Posted February 5, 2015 Share Posted February 5, 2015 Look into the EFR series if you dont think twin scroll is worth it. If you run a gt30 with a twin scroll housing slapped on vs single scroll there may not be as much of a difference. Link to comment Share on other sites More sharing options...
Underdog Posted February 5, 2015 Share Posted February 5, 2015 I would not say the TS is more "driveable" - it is just slightly different. My TD04HLA-19T setup had such a low boost threshold and such fast reponse I could never really accelerate without boosting, which made the car feel a little spastic. Couple that with the fact that it is a small turbo (in "stage 2" trim I was making VF40 numbers - ~240whp) that falls on its face in upper RPM and it was very disappointing from the "wannabe turbo sports car" perspective. On the daily commute it was fun to be able to go light-to-light, but any time I could really open it up I found myself wanting more. On single scroll 1.5XTR cars I have driven the car feels very sedate when you are putzing around town. Once you get into the mid-3k rpm range and punch it though - the boost builds very quickly and the torque puts you back in the seat. I have come to appreciate sacrificing a bit of low-end response for the wider mid/upper-range power. I believe that the TS setup gets you the best of both worlds, but it has to be a diminishing return. Since you already have a bunch of parts it is a bit easier to justify - but you are still talking a multi-thousand dollar project to stretch your torque curve slightly to the left. I PnP'd my B25 heads myself (very light bowl work and runner cleanup) before having the exh. runners and chambers/valve heads coated by SwainTech. I like the B25 heads because the larger chamber gives a lower compression ratio, all else equal. Purists tend to not prefer them over the D/V/W-style heads which have a smoother chamber profile and more meat for true porting (changing the volume/shape of the runners), but since I am going with a medium-size stock-location turbo and TMIC it really wasn't important to chase peak flow numbers with the heads. The Crimson Dynamo Link to comment Share on other sites More sharing options...
dahoseman Posted February 6, 2015 Author Share Posted February 6, 2015 It sounds like you have some decent experience with various setips. Any opinions on the EFR turbos vs the blouch Dom's? I have read a few fantastic reviews of the EFR turbos, after looking into them. In fact, some reviews are a bit "too" fantastic that I'm skeptical of the reviewers Link to comment Share on other sites More sharing options...
Underdog Posted February 7, 2015 Share Posted February 7, 2015 I haven't built or driven a car with an EFR setup yet. Let's back up a bit - what fuel will you be running? Do you plan to run an FMIC or stay TMIC? Do you plan on building the engine? You mentioned that the STI will be play & DD - what does that mean in terms of the way it will be used and how much time/money you are willing to put into maintenance? The Crimson Dynamo Link to comment Share on other sites More sharing options...
dahoseman Posted February 8, 2015 Author Share Posted February 8, 2015 I haven't built or driven a car with an EFR setup yet. Let's back up a bit - what fuel will you be running? Do you plan to run an FMIC or stay TMIC? Do you plan on building the engine? You mentioned that the STI will be play & DD - what does that mean in terms of the way it will be used and how much time/money you are willing to put into maintenance? fuel: I will be running pump gas, tuning for 91 octane so I don't have to worry about where I have to fill up. Intercooler: The car is still on the stock STI TMIC. I plan on sticking with a TMIC, but I may install an aftermarket version. Internals: I was debating whether or not to replace bearings/studs/pistons, but I don't currently plan on adding anything further to the engine. I'd like a healthy and wide-as-possible torque curve around 330-350 wheel torque. Driving: This is a bit tricky as my driving requirements and driving locations change frequently. First and foremost, it will never be used on a track. For the most part, it will be a commuter in city traffic. I do make multi-hour highway trips up to 3 times per week. However, for a month-or-so at a time (several times throughout the year) I will need to use it for interstate travel while hauling my personal gear for occasional forays into the woods. Money/Maintenance: I'm going to set an overall 'mod' budget of $5k. I plan on modifying the suspension (raising it slightly, actually), so that will take some of the budget. I will likely sell the aftermarket parts that I take off of the car. For the most parts, whenever I get a new-to-me vehicle, I try to re-engineer various components and factory deficiencies so that they don't need constant maintenance. I don't mind a car that is a little 'prissy', but I like to install stronger components to begin with and take care of preventative maintenance early on. I'm wondering if I should just install my VF36 twin scroll setup that was rebuilt with ceramic bearings and billet wheel ...... which I already have sitting around. I'm not sure the Blouch would do anything better for my needs. I don't know though. Thoughts? Link to comment Share on other sites More sharing options...
Underdog Posted February 8, 2015 Share Posted February 8, 2015 First - I get where you are coming from with your approach to modifying the car. This is more-or-less the usage and mindset I had when I first installed my 19T twinscroll back in '08/'09. The reality is that with the parameters you've set, anything larger than an 18G is going to be under-utilized. Sure the 1.5XTR can make good power but it is designed for higher pressure ratios than 91/93 octane can support without going to an unreasonably low static compression ratio in the engine. Therefore the 1.5XTR is really only going to get close to its sweet spot (~24-26 PSI) if you run E85 or meth injection. All that being said, the 1.5XTR is still a great turbo for pump gas and TMIC setups (which is why I chose the TS variant for my build, for the times E85 is not available). Now, sure you could swap out your very good 1.5XTR setup for something that gives you a tiny bit more low end at the expense of some upper range power, but you have set a limit of $5k as an overall mod budget which I assume includes the suspension work you mentioned, any finishing touches to the power setup (including a tune), and possibly rebuilding the engine and/or addressing any other unexpected maintenance items on your older Subaru along the way. What this says to me is that it would be absolutely nuts to put any money towards replacing good parts. In the end you will have to do the calculations to determine if you can sell off unused parts to offset the cost of whichever path you choose. I realize that the heart wants what it wants, so I'm not trying to convince you to take a particular path. There will be plenty of opportunities to optimize (spend money on) the single scroll 1.5XTR setup. BTW - the '08+ STI TMIC is plenty capable of supporting an octane limited 1.5XTR. This is another area where there would be negligible benefit to going with a pricey aftermarket unit (and even more so with an inexpensive aftermarket unit). The Crimson Dynamo Link to comment Share on other sites More sharing options...
dahoseman Posted February 8, 2015 Author Share Posted February 8, 2015 Thanks for the information. I think you're right on the Dominators in general. For my goals, they're overkill for potential power and underutilized for actual power. Having said that, I'm still considering replacing the exhaust/turbo with the pretty slick setup that I collected over the last few months. I have the JDM twin scroll header and was told that the VF36 has slightly better flow characteristics than the VF52. My VF36 is rebuilt with a billet wheel that flows 20% higher flow and has ceramic bearings. If I don't install it, then I should sell it instead of letting it sit around. Link to comment Share on other sites More sharing options...
Underdog Posted February 8, 2015 Share Posted February 8, 2015 I don't think you will be disappointed with the VF36. I can't speak to the billet wheel or ceramic bearing upgrades, but in original form that is a very nice turbo. Your top end will not be as strong as the 1.5XTR but it should have a considerably lower boost threshold due to the smaller hot side. Personally I would still stick with the single scroll 1.5XTR given everything you have said, but as I mentioned earlier - I would prefer to have the boost come on a bit later and hold strong to redline rather than have the power taper off. If you do decide to install your twinscroll kit then I would suggest holding on to the Dom until you have lived with the VF36 long enough to know you love it. The Crimson Dynamo Link to comment Share on other sites More sharing options...
dahoseman Posted February 8, 2015 Author Share Posted February 8, 2015 I don't think you will be disappointed with the VF36. I can't speak to the billet wheel or ceramic bearing upgrades, but in original form that is a very nice turbo. Your top end will not be as strong as the 1.5XTR but it should have a considerably lower boost threshold due to the smaller hot side. Personally I would still stick with the single scroll 1.5XTR given everything you have said, but as I mentioned earlier - I would prefer to have the boost come on a bit later and hold strong to redline rather than have the power taper off. If you do decide to install your twinscroll kit then I would suggest holding on to the Dom until you have lived with the VF36 long enough to know you love it. That's not a bad plan. If I do the swap, I'll have to figure out where to get tuned. I'm thinking of driving a little north of NY for that one. Link to comment Share on other sites More sharing options...
Glack Posted February 16, 2015 Share Posted February 16, 2015 My opinion, go twin scroll, be different Does twin scroll make that big of a difference? In spool and power delivery, absolutely just depends on the setup. Below is probably a little further than what your looking to do, but it's a great example. Both runs are my car, same built motor, same fuel (e85), same dyno, same tuner- only difference was turbos and headers. The FP green was 7cm and ported and polished by grimmspeed, single scroll. The other is a FP HTA 86 1.00ar twin scroll. The fact that this much(MUCH) larger turbo than a FP green(and the Green is maxed out on this run, was just curious of its capabilities) is only about 2-300 rpm slower than the FP Green speaks volumes as to the ability of twin scroll. Link to comment Share on other sites More sharing options...
rdhayward Posted February 28, 2015 Share Posted February 28, 2015 I would not say the TS is more "driveable" - it is just slightly different. My TD04HLA-19T setup had such a low boost threshold and such fast reponse I could never really accelerate without boosting, which made the car feel a little spastic. Couple that with the fact that it is a small turbo (in "stage 2" trim I was making VF40 numbers - ~240whp) that falls on its face in upper RPM and it was very disappointing from the "wannabe turbo sports car" perspective. On the daily commute it was fun to be able to go light-to-light, but any time I could really open it up I found myself wanting more. ... I have Underdog's system installed in my '06 Spec B, SPT exhaust, Cobb AP, hit 206 hp & 287 tq on a Mustang dyno (with some clutch slippage). I share his impression of its driving characteristics. It's a stock Subaru turbo, but renders silky smooth power compared to the VF40. Definitely a performance upgrade even if the numbers don't bear that out. Plus, I'm glad it's essentially an OEM system (except for the AVO catted downpipe necessary to this conversion). Link to comment Share on other sites More sharing options...
dahoseman Posted March 6, 2015 Author Share Posted March 6, 2015 Thanks for the information and personal experience with these. I'm still quite torn on what to do. 1. On one hand, I already have a set of JDM twin scroll headers with a VF36 twin scroll turbo remanufactured and upgraded by SixStarSpeed (ceramic bearings and billet 7/7 wheel which supposedly flows 20% more air). 2. On the other hand, the car I'm picking up already has a single scroll Blouch Dominator 1.5XTR on stock UEL headers with a custom-welded EWG. I was planning on tuning for 91 octane because I travel to the 'sticks' a lot and I want the car to be tuned for the worst case scenario of not having higher octanes available for a while. However, I think I have been convinced to tune for 93 octane with a detuned 91 octane 'emergency' map. I have been told that the Dominator is essentially useless on 91 octane because it never even gets into its efficiency range, but I don't have any real experience. Any thoughts on the single scroll vs twin scroll versions of the Dominator 1.5xtr? Link to comment Share on other sites More sharing options...
Guest Posted February 10, 2017 Share Posted February 10, 2017 Bump? OP never updated the thread.... I have a twinscroll setup with a hybrid VF36 & GT2871. I really like it - not just for fast spool-up but also for the sound - but that's a function of EL headers. Here is my old dyno chart: http://legacygt.com/forums/showthread.php/twinscroll-vf36-gt2871-hybrid-dyno-tune-results-127433.html The issue has been getting smooth tune - the relocation of the stock wideband is causing weird oscillation, that can be disabled only by killing rear O2 sensor. Our ECU does not expect the sensor to be further away. I know folks later discovered some logic in the ECU responsible for it, but I do not know if these tables were ever reverse engineered. I've been planning an upgrade to 1.5XTR-TS - even bought a turbo housing for it and got it coated. However, never finished the plan - in fact the car has been parked for 3 years... will be "restoring" it this spring. Link to comment Share on other sites More sharing options...
Th3Franz Posted February 10, 2017 Share Posted February 10, 2017 I have a twin scroll EFR 7163. Twin scroll shines more with bigger turbos and especially large, lightweight turbine wheels like the EFR. A dyno plot doesn't show the benefit as much. But driving my car I don't even think about turbo lag. Hit the pedal at sufficient RPM and boost comes on fast and hard. I'm working through some brake issues on the car and then need to do a retune on ACN 91 gas... I'd like to make a video of how the car sounds and the boost response. It's pretty unique for a Subaru imho. -Franz The end of a Legacy http://www.youtube.com/th3franz Link to comment Share on other sites More sharing options...
Rhitter Posted February 10, 2017 Share Posted February 10, 2017 Th3Franz, did you move here recently? Looking forward to see your car some day. There are a few of us in the Bay area now. @Unclemat - Underdog went with a 1.5xtr-ts, I think he said he should have just done a 1.5xtr. So maybe talk with him a little before proceeding with your plan. My OBXT build Link to comment Share on other sites More sharing options...
Guest Posted February 10, 2017 Share Posted February 10, 2017 ^ Yup, I did, but he did not quite elaborate on the issues. The ongoing issue I had with twinscroll tune was a constant oscillation on steady throttle around 3k rpm. I think it has to do with the remote relocation of the front O2 sensor. I hope that zeroing AF3 correction limits (see this romraider thread) may help. For me the only way to eliminate this oscillation was to actually disconnect *rear* O2 sensor. My car is twinscroll already so 1.5XTR TS is a bolt on affair - I have all supporting mods already. Going single scroll would be more hassle... would need headers/up/dp. Anyway, the ultimate mod I am planning is adding a CTS-V manual wagon to the stable, so I may just keep on driving my VF36-GT2871 hybrid in the LGT, especially if I fix the tune issues Link to comment Share on other sites More sharing options...
Rhitter Posted February 10, 2017 Share Posted February 10, 2017 I just realized this was where Underdog talked about 1.5xtr v ts. So duh on my part.... Completely unrelated - I think I have your old JDM front springs on my car Unclemat. I got them from BAC5.2. JDM Spec.b Rev C wagon springs I think. My OBXT build Link to comment Share on other sites More sharing options...
Guest Posted February 10, 2017 Share Posted February 10, 2017 ^ Many people have suspensions that passed through my hands Link to comment Share on other sites More sharing options...
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