EcoBoost Mustang Exhaust Update

If you’ve been keeping up with our R&D updates, you know that EcoBoost Mustang Hard parts development is chugging along.  A Stage 1 power package is just around the corner with additional stages coming soon!  Here’s a sneak peek at a our Turboback Exhaust which will be offered as a part of the advanced stage packages.

2015 STI Development : Staged Power Package Evaluation

2015 Subaru STIAs 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.

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

COBB R&D Update : February 2015

Here’s a quick peak at what our Engineering Team is working on for February!  Big projects include Ecoboost Mustang Turboback Exhaust, 2015 WRX Intake/Airbox Combo, and a COBB Exclusive – Accessport adjustable Traction Control!

Buy an Accessport V3 and a Turbo-back exhaust might be on us!

With Formula 1 happening this weekend in our own backyard at COTA, we want to give you F1 fans a little incentive to get your vehicle to the next Stage with the COBB Accessport V3.


Purchase (or Upgrade to) an Accessport V3 between now and October 31st , Noon CST, and you may find yourself getting a FREE COBB Turbo-Back Exhaust to go along with your Accessport!


Three winners will be selected at random and contacted the week of November 3rd for fitment and shipment info.  Good luck!

Subaru Tuning – A Quick Look into Boost Creep


Boost creep is something we tend to address quite a bit during the winter months.  Below we will go over the causes of boost creep, why you should be aware of it, and solutions to keep your boost levels in check.

Boost creep is defined as a condition of rising boost levels past what the predetermined level has been set at.   For example, if your target boost level is 15psi, you would see the boost levels increase beyond that as RPMs increase.  The short explanation for boost creep is that the wastegate is not able to flow enough air to bypass the turbocharger’s turbine housing.  When the volume of air flowing through the turbine housing continues to increase, boost will also continue to increase.  Boost creep is most commonly observed in areas that have very low ambient temperatures as well as high atmospheric pressure.  This often encompasses those in the Pacific Northwest as well as New England and East Coast.


Boost creep is undesirable for a number of reasons.  When a car exhibits a large amount of boost creep it makes controlling the boost level next to impossible for a tuner.  A car that is on the edge can exhibit highly variable boost response under different environmental conditions.  For instance, if you have your car tuned during warmer months, the change in weather going into winter may be enough to cause a significant increase in boost.  Once the flow limit of the wastegate has been reached, exhaust gas back pressure will increase.  This is very inefficient and will cause temperatures to increase and introduce more detonation-prone conditions.

Boost Creep is not a condition that can be corrected solely by making tuning changes as it is a mechanical limitation.  The two easiest ways to address boost creep are to either port the wastegate housing of the turbocharger in order to allow it to flow more air or to switch to an external wastegate style uppipe.

If you’re looking for answers to other tuning related questions, head over to our Knowledge Base!

COBB Releases BMW Stage 1+ Front Mount Intercooler and Stage 2 Downpipe with OTS Map Support

COBB is proud to announce the release of our BMW Front Mount Intercooler and N55 Downpipe along with off-the-shelf map support!

COBB BMW 1 & 3 Series N54-N55 FMIC Kit

COBB N54/N55 FMIC – One of the best power modifications for your BMW 1 or 3 Series – Click here for more pictures and details.

COBB BMW N55 Downpipe Kit

COBB BMW N55 Downpipe – Take your N55 powered BMW up to Stage 2! Click here for more pictures and details.

Tune your ECU for these modifications using our off-the-shelf maps!


2011 Subaru STI 12.4 sec. ¼ Mile using COBB OTS Maps!

10 years ago, Darius lined up his 2000 Ford Escort ZX2 with a shot of nitrous and some bolt-ons to pull a 14.37 at 96.9 MPH. Since then, he’s been hooked on drag racing with a variety of cars and recently ran a 12.42 at 109.4 MPH using only a 2011 Subaru STI Sedan with help from a COBB Downpipe, a COBB SF Intake and Airbox, and a COBB AccessPORT running off-the-shelf (OTS) Stage 2+SF mapping.

Time Slip

After setting the record for the fastest stock turbo, manual transmission diesel truck in his 2004 Chevy Silverado 2500HD Duramax Diesel, Darius decided a 2011 STI sedan was the perfect comprise of speed and comfort. He missed his old 2005 STi and couldn’t pass up a fast 4 door that featured Bluetooth, heated seats, and integrated iPod controls. To make his fast 4 door even faster, he opted for a few choice COBB parts. The AccessPORT with datalogging and preloaded maps for various modifications made tuning easy, the SF Intake added some power and sounded great, and the used COBB Downpipe mated up to the stock exhaust perfectly.

Engine Bay

With just $1200 spent on modifications and some excellent driving, Darius was able to run a 12.42 at 109.44 MPH with a 1.686 60′ time. And to prove it was no fluke, he followed it up with a 12.44. Next season, Darius hopes a few more modifications, some custom tuning, and experimentation with the Launch Control and Flat Foot Shifting features built-in to the AccessPORT will get him down to the 11 second range.

If you’d like to learn more about the AccessPORT, the COBB SF Intake, the COBB Downpipe, or any of our other products, just visit

Darius STI

COBB Tuning 08+ Nissan GT-R Downpipes Available Now!

COBB Tuning introduces the 3” Stainless Steel Downpipe Kit for 2008+ Nissan GT-R vehicles. These stainless steel units are the same downpipes that helped power our COBB Motorsports Redline Time Attack Modified Class GT-R to a Class Championship in 2010! Designed to bolt up to the stock turbos or stock-location upgraded turbocharger kit, this downpipe kit has been rigorously track-tested and proven reliable at power levels beyond 800whp.

Take your Stage2 GT-R with upgraded Y-Pipes to the next level with the COBB Tuning 3” Downpipe Kit. Consistently improve turbo spool-up by 250-300RPM and open the door to maximum stock turbo power output when coupled with complementary modifications including; injectors, fuel pumps, intakes, boost tubes and intercoolers.

These high-flow, mandrel-bent, 304-stainless downpipes remove the restrictive stock catalytic converters for better flow, faster turbo-spool and improved transient response. This downpipe kit is a direct OEM replacement and will bolt up to the stock exhausts system or aftermarket systems alike.

For more information on the COBB Tuning 3” SS Downpipe Kit for the 08+ Nissan GT-R, please visit our website at or call toll free at 1-866-922-3059.

COBB Tuning Dominates Redline Time Attack Round 4 at Auto Club Speedway

The COBB Tuning Motorsports team dominated Round 4 of the Redline Time Attack series at Auto Club Speedway in Fontana, California, taking 1st in Super Modified AWD, 1st in Modified AWD, 1st in Street Tire AWD and capturing the Overall Event Win. The Super Session wheel-to-wheel race was an exciting inter-class battle and saw the Nissan GT-R win overall in Modified trim and the STI take the Street Tire class win. In addition to bringing home maximum points, Brian Lock set a new track record for a Modified Class car at Auto Club Speedway in the GT-R with a lap time of 1:43.072.

In a bid to appease the “Racing Gods,” the team showed up sporting COBB-blue hair-dos, but the success of the weekend was a direct result of the long hours and tireless effort put in by the talented and dedicated guys that make up the COBB Tuning Motorsports crew. The team took advantage of the month-long break between events and made significant changes to all three race cars in an effort to maximize performance and reliability, ultimately setting the team up to race hard for the remainder of the season.

The Nissan GT-R was treated to a complete engine rebuild with upgraded rods and pistons to better cope with the nearly 1,000 crank HP being produced. The Subaru STI went under the knife having a new custom safety cage fabricated from scratch and the transmission rebuilt while the Cosworth engine was sent home for a refresh and new Cosworth intake manifold added. The Nissan 370Z received a new set of rear springs to reduce excessive corner-exit oversteer. Finally, all three cars had OS Giken limited-slip differentials installed (GT-R front, STI & 370Z rear) to better get the AccessPORT tuned power down on the track where it belongs.

The extensive hours of hard-work paid off in spades as the team racked up its most successful weekend to date in the Redline Time Attack. Brian Lock in the Nissan GT-R screamed past the competition to take the Modified Class win and set a new track record of 1:43.072 in the process. After setting the new record, the GT-R visited pit lane to receive a new set of Yokohama A005 racing slicks before heading right back out on track to battle it out in the Super Modified class. The added grip of the Yokohama slicks dropped the GT-R’s lap time to a 1:39.730, fast enough to take the win in the Super Modified class and clinch the team’s second Overall event win!

photo courtesy of

In the Street Tire AWD Class, Cameron Benner was on a mission to grab the 1st place position that had so far eluded him. The revitalized Subaru STI proved to be the perfect tool for the job as Cameron charged ahead the rest of the Street Class field, taking a decisive first win with a 3-second lead over his closest competitor!

photo courtesy of

Gary Sheehan subbed in for an ill-feeling Trey Cobb to take on the Nissan 370Z driving duties. Although Gary was ineligible to compete in the Enthusiast Class, the event presented an opportunity to see how the suspension and driveline changes affected the performance of the little Z, and they proved to be quite effective. The COBB 370Z turned a time just 0.5 seconds shy of the Enthusiast RWD class winning lap in the final Time Attack session, and also revealed a few simple areas of improvement that, once addressed, should make it a serious class contender.

photo courtesy of

The wheel-to-wheel Super Session turned out to be an exciting inter-class battle that once again showed that solid preparation, nerves of steel and blue hair will take the day. Brian Lock ran the Nissan GT-R in Modified trim with R-compound tires and gapped the field to take the overall win and much-needed Modified class championship points. Cameron Benner had a great drive in his Street Tire Class STI, battling with Modified class cars on the way to his class win and 4th place overall, adding to his impressive championship lead.

The Takata Time Attack/LIC Motorsports STI, had a strong showing this weekend, taking 2nd place in the Modified AWD Class with a 01:45.923 lap time and 2nd place in class in the Super Session . This car runs a COBB AccessPORT and was tuned at COBB Tuning Surgeline in Portland, Oregon. The LIC Motorsports team continues to show what quality preparation and great tuning can do as they consistently field the fastest Modified Class Subaru in the series and currently lead the Modified Class championship.

Jon Drenas showed what a lightly modified Mitsubishi EVO X can do by finishing in 2nd place in the AWD Street Class. Jon arrived at the track late in the event and laid down a 1:52.702 lap with almost no practice time in his HB Speed-tuned AccessPORT EVO X. Jon and his EVO X is a force to be reckoned with on the West Coast and has proven that you can drive your race car to the track, race it all weekend, and drive back home with a trophy in the passenger seat.

Chris Billedo drove his AccessPORT equipped Honda Civic Si to the sharp end of the Enthusiast FWD class with a solid 2nd place finish, continuing his streak of podium finishes and setting himself up for an impressive Redline Time Attack championship result.

The COBB Tuning Motorsports Team next heads to Autobahn Country Club in Joliet, Illinois for Round 5 on June 12th where they look to extend their East Coast Championship leads in the Modified and Street Tire classes.


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The Battle of the Bayou, Two Lousiana EVO X’s duke it out at COBB Tuning Plano

Two EVO X GSR’s, Two friends, Similar setups, different sets of cams, different downpipes, 875 combined wheel horsepower, one tuning shop.

In February, COBB Tuning Plano tuned James Stearns’ EVO X GSR running a Forced Performance “Red” turbocharger, it made good power gains over the stock turbo, but we knew the car had so much more potential. A set of good camshafts would be needed to make the car work with the bigger turbo more efficiently. A set of Kelford 214b cams were ordered knowing that they would do just the trick!

Not to be outdone by his good friend, James, Dustin Nelson decided to step it up and purchase a FP Red for his EVO X as well. Duston also upgraded to the COBB SS Downpipe and decided on the Cosworth MX-1 camshafts.

Both agreed to come drive up from the Bayou of southern Louisiana and drop off their cars for a few days, anticipating some very impressive gains. James started with 377whp and 361ft-lbs of torque, while Dustin’s car weighed-in with 331whp 378ft/lbs. After the installations, James was first up on the dyno and netted a gain of 57whp and 34 ft/lbs making this car the most powerful EVO X at COBB’s facilities in Plano at 434WHP and 395WTQ at 27psi on 93 octane gasoline!

That record would be short lived though, as 26 hours later, COBB Tuning Plano’s lead tuner, Calvin Dotson, made 441WHP and 393WTQ on the same boost pressure of 27 psi and on 93 octane out of Dustin’s Octane Blue Pearl EVO. This set a new bar of power achievement on any EVO X in COBB’s dyno database and netted 110whp over his previous setup!

Congratulations to these two guys, we bet the drive back home was incredible!