2015 STI Development : Staged Power Package Evaluation

2015_Subaru_STI_Keith-Treder-2_blog

As you may know, one of our public commitments following the release of the new 2015 model year VA-series chassis code Subarus (2015+ WRX and STI) was to thoroughly explore each platform and quantify our findings whenever possible.  Because the 2015 STI retained a very similar mechanical configuration to the 2008-2014 STI (GR-series chassis code), many in the community have anticipated that hardware and tuning options would be identical to the current offerings.  The idea behind our testing was to discard any existing assumptions about how the 2015 STI may compare to its older brothers and make sure that we are providing hardware and tuning solutions that exceed expectations.

Two of the prevalent issues with the GR series WRX and STI have been a “Boost Creep” problem and a fuel system that is at or beyond capacity on cars that are equipped with a turboback exhaust, especially when combined with an upgraded free-flowing intake.  This topic was previously discussed here: Subaru Tuning : A Quick Look into Boost Creep.

The key item of significance here: Airflow increases must be met by increases in fuel flow – AFR is a ratio air against fuel, by definition, and thus they must increase proportionally with each other.  We’ve previously explored how adding an intake increases airflow on the 2015 STI in a previous article, available here: 2015 Subaru STI Development Update – COBB SF Intake Testing.

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COBB Tuning’s 2015 STI undergoing dyno testing a COBB Tuning Surgeline in Portland, OR

Goal:  Analyze fuel system performance when attempting to tune for a COBB Turboback Exhaust and COBB SF Intake System on a 2015 STI.  Will the factory fuel system be adequate to support this setup?

Vehicle:  COBB Tuning R&D 2015 STI (#2).  ~900 miles on odometer.  92 octane pump gas.

Method:  In order to gather numerical data for analysis, we collected datalogs from the car under wide open throttle (WOT) dyno runs, in the following tune/hardware configurations:

  • Stock (S#); Stock
  • COBB v340 Stage1 93 OTS (S#); Stock
  • COBB v340 Stage2 93 OTS (S#); COBB Turboback Exhaust
  • COBB v340 Stage2+SF 93 OTS (Experimental) (S#); COBB Turboback Exhaust + COBB SF Intake System

Conditions:  45-48 degrees F, Sea Level elevation.  COBB Tuning Surgeline, Portland, OR.

Background:  In general, while performing aftermarket tuning, a fuel injector is considered to be at their flow limits once reaching ~95% Injector Duty Cycle (IDC).  Beyond this, the amount of “off” or non-driven time for the injectors between injection events is inadequate for allowing the electrical coil within the injectors to fully discharge.  With this, the beginning of the next injection event comes earlier than anticipated, as the injector is already partially charged when the ECU begins driving it for the next injection cycle, and the net result is a flow non-linearity (usually demonstrated as a brief rich dip in air-fuel ratio).  After passing roughly 105% IDC, even with this rich-leaning non-linearity, the total window for injection in terms of time is now simply too short, and an inadequate amount of fuel is delivered to maintained the desired air-fuel ratio, so air-fuel ratios begin to go lean of targets.

What does this mean?  Past ~95% IDC, we mechanically lose control over fueling and air-fuel ratio will not be on-target.  Dangerous lean conditions will result past ~105% IDC.

Things to keep in mind:  Air density is a critical factor.  We intentionally tested in Portland winter months, where temperatures are cool and atmospheric pressures are high.  At elevation and high ambient temps, the concerns mentioned above become reduced as air mass is reduced.  Keep in mind, however, that it was still in the mid 40’s during this testing.   Injector Duty Cycles could easily be 5-15% higher if the testing were completed in a much colder area around the United States, such as New England, which has seen a long period well below frozen this winter.

Results:  OK, time for the relevant stuff.  This chart shows the logged Injector Duty Cycle during a full-throttle dyno run for each of the aforementioned configurations.  We’ve added a red line showing the 95% threshold we would ideally like to stay below.

Graph of Injector Duty Cycle (Y-axis) against Engine Speed (X-axis) for each configuration
Graph of Injector Duty Cycle (Y-axis) against Engine Speed (X-axis) for each configuration

As we can see, the issue is already borderline on the completely stock vehicle.  Subaru targets an extremely rich air-fuel ratio and the 2015 STI has been observed to be the most powerful STI to date; one has to wonder why they have not upgraded the fuel system’s capacity to match this.

With tuning (Stage1), we see that peak values are similar to stock.  We are targeting a leaner AFR but using more boost/airflow to make more power, so overall total injector usage remains similar.

At Stage2, we’re really getting up there.  The fully upgraded post-turbo exhaust hardware facilitates more airflow and we use even more injector as a result.  No NASA scientists needed on this one!  However, while Injector Duty Cycle does definitively now exceed 95% for a good portion of the run, it stays around 100% peak.  We have lost control of fueling, but we probably are not going to induce lean conditions yet, meaning the engine should not be at any significant new risk.

Stage2+SF: Uh-oh!  Now that the intake side has been freed up, we’re using a LOT more injector.  With Injector Duty Cycles peaking around 107%, we can no longer be sure that there is enough fuel available to keep a ball-park safe air-fuel ratio, let alone precise control over it.

As mentioned earlier, this would only get worse as ambient temperatures go further downwards.  While mid-40’s is definitely cold for all of the Arizonians reading along, Michigan residents are likely nodding along in full agreement.  Much of the U.S. sees sustained temperatures well below 40 F during their colder periods of the year.

Summary:  So, where does this leave us?  In short, it means that we (COBB Tuning Subaru Experts) are not comfortable offering “Stage2+SF” as a released stage package for the 2015 STI.  We know this is likely to disappoint some and confuse others, especially since the package is still offered for the GR vehicles.   However, not all is lost.  Thanks to our partnership with Injector Dynamics, we are well-positioned to now offer OTS packages that include fueling system upgrades, which have typically been “custom tune only” territory for Subarus.  Be on the lookout for an upcoming COMPLETE Stage3 package for 2015 STI that includes fuel system solutions in addition to full turboback and intake hardware!


COMMENTS
basel hamad on February 18, 2015 says:

I have a 2015 STI with Stage 2. Let me know if I can be a beta car for the stage 3 setup!

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Kevin on February 24, 2015 says:

So how is the 2015 WRX Intake/Airbox Combo coming along? With the last blog update I thought it was being released in February. Oh well, just excited to see the power gains you guys pull off with it. Was real curious on the ballpark power gains you are expecting with the intake on the FA engine.

Reply
    Marshall
    Marshall on February 25, 2015 says:

    Hey Kevin, we’re still working on our intake design for the 2015 WRX and are hoping to have something available in the near future. As has been true with the Subaru platform for some time, the power gains from simply adding an intake are marginal. Our main goal with Subaru intakes is to reduce pre-turbo restrictions allowing the turbo and engine to make power more efficiently.

    Marshall@COBB

    Reply
Derek on February 26, 2015 says:

When do you think Stage 3 will be release for the 2015 STi, I’m happy to work with you on testing – I’m up in the Northeast

Reply
    Marshall
    Marshall on February 26, 2015 says:

    Hey Derek,

    We’ve been testing on our shop 2015 STI up in Portland and results are very promising! Hoping to have a that power package available in March!

    Marshall@COBB

    Reply
Jason on March 3, 2015 says:

Will the fueling upgrades include the Cobb regulator kit? How about adding the EBCS to the 2015 OTS maps as well?

Thanks!

Reply
    Marshall
    Marshall on March 3, 2015 says:

    We will definitely offer a Staged Power Package that includes the FPR kit. Not sure about the plans for OTS support for EBCS, the factory solenoids are quite good on the newer cars so an upgraded part is not needed right away.

    Marshall@COBB

    Reply
pushinpsi on March 3, 2015 says:

Hi,

I just bought my first sti, and I was wondering what would be the best bet for intake and exhaust from cobb ? Its a 2008 hatch. Ive read that I have to have it tuned even if its just a Cobb intake. Is this true?
Thanks,

James

Reply
    Marshall
    Marshall on March 3, 2015 says:

    Hey James, you’ll definitely need to have the car tuned whenever making changes to the intake. Any time you alter the way air flows over the MAF sensor the ECU will need to be properly calibrated. We do offer Off The Shelf maps that will support our COBB SF Intake and the AEM Cold-Air Intake systems for your vehicle. If you were to add an Accessport into the mix you would have those maps as a solution!

    Marshall@COBB

    Reply
Joe on March 3, 2015 says:

What type of power are you looking at getting in your preliminary tests with the Stage 3 Package for the 2015 STI?

Reply
    Marshall
    Marshall on March 3, 2015 says:

    We don’t have any dyno sheets to show quite yet but numbers are looking promising. Expect a nice jump in low-end torque and the ability to carry more power towards redline with the added fuel capacity.

    Marshall@COBB

    Reply
Nick Batsch on March 4, 2015 says:

What are the numbers for the fuel pressure required with just the air intake cobb access port tuner and blow off valve stock STI exhaust. I ordered my access port tuner and I am in colorado at 5500 feet. we only have 91 octane here and I would be putting the cobb air filter and box with a stage 1 tune at 91 octane here in Colorado at 5500 feet. do you think i will need to upgrade my injectors and fuel pump to handle that small of a change
thank you

Reply
    Marshall
    Marshall on March 4, 2015 says:

    Hey Nick, you should be just fine with that setup in your location. As you’re probably aware, there is a bit less oxygen at that altitude so the fuel requirement is also a touch less. Our Stage1+SF map should be just fine for your car. If you’re concerned at all, feel free to send a datalog over to support@cobbtuning.com for us to evaluate.

    Marshall@COBB

    Reply
Tony rodriguez on March 4, 2015 says:

Where can i find the stage 2 maps for STI 2015 with a AEM cai, I have the access port with a DP stock intake for now and have the CAI waiting for a map

Reply
    Marshall
    Marshall on March 5, 2015 says:

    Hey Tony, we do not currently offer an OTS map to support an AEM intake on the 2015 STI. I do not believe we have plans to support that intake using our OTS maps so your best bet would likely be a custom tune.

    Marshall@COBB

    Reply
Rumor(???): Cobb designing Focus ST aux fuel system on March 6, 2015 says:

[…] speaking about 2015 STI development I'm pretty sure. They recently had this write up on their blog: 2015 STI Development: Staged Power Package Evaluation. They will probably be offering fuel system upgrades for the STI in their Stage2/3 packages. […]

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andrew on March 10, 2015 says:

So what i gather here is that I should hold off getting any kind of turbo back exhaust parts for my 2015 STI if I leave my Cobb SF intake on with Accessport until there is a MAP and fueling resolution…correct?

Reply
    Marshall
    Marshall on March 10, 2015 says:

    Correct. The stock fuel system can handle an intake OR turboback exhaust, but not both. We’re finalizing some details with our Stage 3 Power Package right now and should have that available here in the next month.

    Marshall@COBB

    Reply
Andy on March 15, 2015 says:

So I have a 2015 STI with an accessport +Cobb SF intake…what you are sayin its NOT safe to add a Cobb downpipe with stock exhaust without a fuel pump upgrade which in the works…?

Reply
    Marshall
    Marshall on March 18, 2015 says:

    Correct, the factory fuel system does not have the capacity to support both an intake and upgraded downpipe. We are developing a Stage 3 Power Package that will include fuel system upgrades along with a downpipe upgrade.

    Marshall@COBB

    Reply
      Eric Feinman on June 30, 2015 says:

      I remember awhile back you were telling people that the 2015 STI could either support a SF intake, or a Down pipe, but not both due to some fuel problems. Has this problem been resolved.

      Reply
        Marshall
        Marshall on July 2, 2015 says:

        It has! We now offer a Stage 3 Power Package that addresses the shortcomings of the factory fuel system. The Stage 3 Package includes upgraded fuel injectors, fuel pump, and a fuel pressure regulator which help to provide an adequate amount of fuel to cover the airflow upgrades(downpipe and intake).

        Marshall@COBB

        Reply
Joe on March 24, 2015 says:

How is the development on the stage 3 package looking? I know it was previously stated you were hoping for a March launch date. Is that still on track?

Reply
    Marshall
    Marshall on March 25, 2015 says:

    We’ve made a revision to our fuel pump and are due to have those in this week for testing. I believe we’re shooting for an April release now!

    Marshall@COBB

    Reply
Victor on March 27, 2015 says:

Hey guys I want to know what the fuel upgrade parts are going to be needed as far as injector brand and size and fuel pump and lines?

Reply
    Marshall
    Marshall on March 30, 2015 says:

    Our Stage 3 Power Package will include upgraded injectors, fuel pump, and our fuel pressure regulator kit.

    Marshall@COBB

    Reply
Charles Whittlesey on April 21, 2015 says:

Any updates on the stage 3 power package?

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    Marshall
    Marshall on April 21, 2015 says:

    We made some adjustments to the fuel pump we will be offering however I believe testing has been completed on the latest revision. Hoping to see a release by the end of this month!

    Marshall@COBB

    Reply
steven whit on May 2, 2015 says:

I know that the stage 3 is not out yet for 2105 sti, but are the fuel components available to purchase now. I don’t see the fuel pump under the products.. would like to purchase products now so I have when stage 3 is released

Reply
    Kyle
    Kyle on May 4, 2015 says:

    Hello,

    The fuel pump components will be available soon!

    Kyle@COBB

    Reply
Kevin Mayo on May 8, 2015 says:

I was wondering what would be included in the stage 3 power package? I know the upgraded fuel pump/injectors/regulator and downpipe is included, but will it be like the other packages that come with the AP + intake/tbe or anything? Trying to plan ahead but I’m sure if I should wait for the package to buy any parts or if I can piece some stuff together now. Thanks!

Reply
    Kyle
    Kyle on May 8, 2015 says:

    Stage 2 will be historical Stage2+SF parts with the addition of fuel injector and pump upgrades.

    Kyle@COBB

    Reply
      basel hamad on May 18, 2015 says:

      Do we have an ETA on the Stage 2+ or Stage 3 package?

      Reply
        Marshall
        Marshall on May 18, 2015 says:

        We’re shooting for this to be available here in the next couple of weeks. We’ve made a last-minute change to a boost reference line for the FPR kit and need to verify that on car before releasing.

        Marshall@COBB

        Reply
          shrimant saxena on May 26, 2015 says:

          what all with the updated kit include/require? intake/downpipe/exhaust/injectors/fuel pump/fuel rail?

          what if you have the SPT catback exhaust?

          Marshall
          Marshall on May 27, 2015 says:

          The Stage 3 Power Package will include an Accessport, SF Intake/Airbox, Turboback Exhaust, Fuel Injectors, Fuel Pump, and Fuel Pressure Regulator Kit. You would be fine to continue using the SPT catback exhaust, you would just want to purchase the rest of the Stage 3 components separately.

          Marshall@COBB

Max Mulder on May 14, 2015 says:

Any updates on the ETA of Stage 3?

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Michael Ralph on May 28, 2015 says:

This package is terribly overdue, iv have been patiently waiting since mid march and still have no idea when to expect this to be released…. maybe brand switch may be in order.

Reply
    Marshall
    Marshall on June 5, 2015 says:

    Hey Michael, I definitely understand your frustration. We’ve unfortunately been dealing with some supplier issues with a few key components for the fuel system upgrades that are required for Stage 3 Power Package.

    Marshall@COBB

    Reply
Philip Willis on June 3, 2015 says:

Hey there, I’ve got a couple of questions for you:
1. Would one be able to run the stage 3 map with the SF intake/box, fuel injectors, fuel pump, FPR, and JUST the downpipe (i.e. just do the downpipe and not the rest of the turboback)?
2. Do you guys plan on making an AOS for the 2015 STi?
Thanks in advance for your response!

Reply
    Marshall
    Marshall on June 5, 2015 says:

    Hey Philip!

    1. Traditionally using a factory catback with other bolt-ons has been okay. We haven’t done any testing with that configuration, however after speaking with our lead calibrator it would likely be just fine. If anything, you may fall a touch short of target boost with the factory catback being marginally more restrictive than an aftermarket system.
    2. We don’t have any current plans to develop an Air Oil Separator. We currently recommend the IAG unit, a number of us have them on our personal vehicles and they perform flawlessly.

    Marshall@COBB

    Reply
Travis Cho on June 5, 2015 says:

So Excited for the stage 3! You guys rock at keeping the roll subaru and I cant say thank you enough! I guess the only way i can fully say thanks is to buy your stage 3 kit!
keep up the amazing work COBB guys!!!! :-)

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basel hamad on June 8, 2015 says:

Are there any power estimates for the Stage 3 yet?

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Joe Sonson on June 11, 2015 says:

Will an aftermarket exhaust manifold be compatible with the Stage 3 map? Any updates on the release?

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    Marshall
    Marshall on June 11, 2015 says:

    Hey Joe, our Stage 3 OTS Map will not be compatible with an aftermarket exhaust manifold, you would want to have the car custom tuned for that configuration. We are very confident in being able to release the full Stage 3 Power Package and OTS map in the next couple of weeks.

    Marshall@COBB

    Reply
Brian Woodring on July 30, 2017 says:

stage 3 map is it available yet ?

Reply
    Marshall
    Marshall on July 31, 2017 says:

    Hey Brian! We are wrapping up development of updated Stage 3 OTS maps and Stage 3 Power Packages. The upgraded packages will include new fuel rails, lines, and the recently released 1050X fuel injectors. I would expect those to be available this Fall.

    Marshall@COBB

    Reply
Jonathan Malashevich on July 8, 2018 says:

So I have been running stage 2 with a Cobb intake and the aftermarket exhaust for almost a year and I nor anyone else has had any problems, or at least noticed any. Do you guys think the car is at risk at all and what do you guys think is the best route of the few options I have?

Reply
    Adam Hill
    Adam Hill on July 9, 2018 says:

    Hi Jonathan,

    It’s certainly a risk to drive a car that is potentially demanding well over 100% IDC at high load. Naturally, the severity will vary from car to car and location to location but it’s not something I would gamble on. There are only two solutions. First would be to upgrade the fuel system and other supporting parts to run our stage3 setup (or some kind of custom setup with a ProTune). Second, I would temporarily revert to the stock intake until you are ready to upgrade other parts later.
    Adam@COBB

    Reply
Adam Burjan on August 14, 2018 says:

Hi Adam,
New owner to wrx/sti last 3 months.
I’m getting a borla catback soon and will get an accessport and have it mapped to stage 1.

When I eventually decide to go to stage 3, I get the required kit you sell, cobb air and the highflow catted downpipe seperately I can then get it all fitted and tuned, is that correct please?

Reply
    Adam Hill
    Adam Hill on August 15, 2018 says:

    Hi Adam,

    Congrats on the new Subaru!
    Ultimately the answer is yes, but there are a few details to keep in mind. Your Borla CBE should fit with our downpipe assuming it fits well with the stock downpipe. Also, since you already have a cat-back and Accessport. Our full stage3 package will include those and can only be sold as a complete unit, but we do sell our fuel system components as their own packages and the intake/airbox as a combo. So you can still save a few dollars by getting those together but just makes sure you compare to the full stage3 so you don’t miss anything.

    Let me know if you have any other questions.

    Adam@COBB

    Reply
      Adam Burjan on August 20, 2018 says:

      Hi Adam,
      Thanks for your reply.
      What horsepower estimation atw would you think I expect on the Access port stage 3 on the stock 2018 ej257 sti motor? And I would expect it to last for at least 70,000 miles reliably, as I wont thrash it. Thanks in advance.

      Reply
        Marshall
        Marshall on August 20, 2018 says:

        Hey Adam,

        Based on environmental conditions (temp, humidity, elevation, etc.) and fuel type, I would expect to see a Stage 3 setup produce right around 300whp and around 330wtq. With proper calibration and maintenance, this setup should definitely be reliable! For more info on power gains and our fueling options, check out this release article: Subaru STI Stage 3 Packages and OTS Maps.

        Marshall@COBB

        Reply