2015 Subaru STI Development Update – COBB SF Intake Testing
So, you’ve probably seen some pretty cool early results from hardware swaps on the 2015 STI platform. But, have you seen any actual data besides some basic dyno charts with really high smoothing? Probably not. Lucky for you, we’re here to provide actual quantified data behind the madness.
Many people were initially disappointed that our first release only included Stage1 maps. This was because we prefer to *thoroughly* test parts to find out what each modification will do so that we can be sure our Staged Package offerings have a definitive gain for your investment. For example, here is a NASIOC thread showing some of the testing we did to compare power output when a downpipe is added to a 2015 STI: http://forums.nasioc.com/forums/showthread.php?t=2639122
For intakes, we decided that looking at only power wasn’t good enough. An age-old claim in Subaru world is that the factory airbox is not restrictive with the stock turbo, and we wanted to see it for ourselves. We put this to the test by measuring turbo inlet vacuum generated on the stock airbox and with a COBB Tuning SF Intake system fitted to the car. Garrett refers to vacuum in the turbo inlet as “depression”: “Any restriction (caused by the air filter or restrictive ducting) will result in a “depression,” or pressure loss, upstream of the compressor that needs to be accounted for when determining pressure ratio.” (http://www.turbobygarrett.com/turbobygarrett/pressure_ratio)
By comparing the depression created by the factory intake against an upgraded intake, we can actually “see” if we have removed a restriction or not. If the depression is the same, well, all we’ve done is added a noise-maker to the car.
To complete this test, we first gathered boost and depression data on the stock airbox using a stock-hardware 2015 STI (tuning only), first on wastegate boost pressures only, then at ~17.5psi peak via our Stage1 93 OTS map in “S#” mode. Next, we gathered the same data on the COBB SF Intake, with no calibration changes other than for the different MAF curve required.
What did we find? Results! The stock airbox creates depression levels of a bit over 1psi on wastegate boost at redline, and well over 2psi on the Stage1 boost levels! What does this mean? Here in Austin, where the elevation is ~800 ft, the barometer was ~14.21psi for the testing day. With the stock airbox at redline, the turbo was only being fed with approximately 12psi of pressure due to the depression. For comparison, this would be the same as running the car at 5500 ft of elevation if there were no depression!
Here is the boost and depression (intake pressure) data for wastegate and for 17.5psi, shown in gauge pressure relative to ambient atmosphere:
As you can see, thanks to the reduction in depression with the upgraded intake, boost is a bit higher on the wastegate. At 17.5psi, we can see that spool has improved and high RPM boost is held out better on the same WGDC settings. In each case, the depression created by the COBB SF Intake system is roughly half of the factory airbox. What does this mean? Simply put, we’ve reduced restriction in the turbo’s inlet path, as shown by the reduction in depression.
I also decided to take this data one step further, which is to calculate the turbocharger’s effective pressure ratio for each case. One caveat is that we’re looking at post-IC pressures, not pre-IC, but because the intercooler has not changed at all between tests, it shouldn’t skew the results too greatly.
Here is the pressure ratio for each scenario (again, baro in Austin was ~14.21psi on testing day), calculated using Garrett’s methodology here: http://www.turbobygarrett.com/turbobygarrett/pressure_ratio
On wastegate boost pressures, we can see that there isn’t too drastic of a difference — perhaps a tenth of a point at very most. However, at 17.5psi, we can see the COBB SF Intake really start to separate itself: pressure ratio is decreased by about two full tenths across the board after spool. What does this mean? The turbocharger compressor is now operating more efficiently, at least in terms of the demanded pressure output (boost) again the amount of pressure available at the input.
So, at the end of the day, here’s what power looks like between the two. COBB SF Intake are the solid lines, stock airbox are the dashed lines:
Long story short? On the 2015 STI, even in otherwise-stock configuration, the COBB SF Intake system (and others that have the same or better airflow capabilities) help the turbo breathe easier and in turn, make the same boost more efficiently or more boost at the same efficiency when compared to the stock airbox.
Thanks for reading along! Hopefully you found this data interesting and helpful. We plan to keep providing results like this as we dig in further on the 2015 STI and WRX, so stay tuned.
Cheers,
The COBB Subaru Expert Group
Wow! Great information on the Cobb intake. I knew there was a slight increase with spool but this proves there is more. The price of the intake pays in it’s own, for performance and for efficiency/mpg!
When will the intake be released for the 2015 sti?
We are working on a revised intake and airbox solution for the 2015 WRX and STI. Unfortunately we do not currently have an ETA, but they should be finalized very soon!
Marshall@COBB
Really NEED this finished and on sale way before October 30th. Already postponed my pro tune to wait for this. Please hurry cobb! My car depends on your cool stuff to go fast and make good noises.
hi i just bought a 2015 wrx sti i want to custom tune the ecu and exhaust how much would that be and how much extra power , and is there a dealer in manila philippines thanks my # 09998836525
Tony, unfortunately our Subaru Accessports currently only support USDM vehicles. Sorry for the bad news!
Marshall@COBB
Hello Cobb .i come form hk!accessports is it can use on my 2015 sti ?when will release stage 2? Becoz I want upgrade my std down pipe to tomei ,is it support?thank you?
Unfortunately our Accessport is currently only compatible with USDM vehicles. It’s possible we will support the 2015 WRX world wide as it is a World Market vehicle however the STI is not. Sorry for any bad news!
Marshall@COBB
I think Hong Kong look like is used ?
Unless the car was imported from North America, the Accessport will not work with your vehicle.
Marshall@COBB
I ask Subaru HK .they say my car is edm…
Jf1 vaf
Ah, unfortunately the Accessport is not yet compatible with EDM vehicles. We are currently investigating offering worldwide support for the 2015 WRX so there is still hope!
Marshall@COBB
guys..my intake is running really hot now with the temperature monitor..please make the box ASAP!!..
We’re on it! Currently hoping to release the airbox in January.
Marshall@COBB
ETA on intake/airbox for 2015 WRX?
I miss the sounds from my 2006 🙁
Hey Sterling, our 2015 STI airbox is set to be released in January with the WRX airbox hopefully not too far behind!
Marshall@COBB
Any update on the Airbox release date?
We’re hoping to have our 2015 STI Airbox available by the end of January!
Marshall@COBB
Cobb, how long until you have a stage 2 tune for the 2015 STI with the Cobb sf intake?? Mine is just sitting there waiting! I need it on! Help! I have the turbo back exhaust and accessport installed and just look at the intake sitting there uninstalled..:(
Tim, our R&D has shown that the factory fuel system is essentially maxed out at Stage 2 power levels. The addition of an intake on top of a Stage 2 setup will require upgrades to the fuel system. Our current plans are to release a Stage 3 package that includes upgraded fuel system components that will allow for further modifications. Keep an eye out for that over the next few months!
Marshall@COBB
Marshall, what would you prefer I’m planning to buy the cobb boost controller Cobb intake and the cobb 1000cc injectors and a dw65 fuel pump should I wait for the stage3 package or just get a protune coz jarred from pdx tuning is coming next month to Hawaii for my 2015 sti
I’m not sure we’ll have the Stage 3 package listed in time for you to get the parts before your tune. If you’re planning to purchase all of the parts together just give us a call and we can put together a custom package for you!
Marshall@COBB
Thank you Marshall for the hook up
No problem, let us know how the tune goes!
Marshall@COBB
I have a 2013 WRX hatchback with the K&N Typhoon intake and Invidia exhaust from the cat back. I was wondering would a tuner improve performance and would it void my warranty.
A tune will absolutely improve the performance of your car! You can definitely use our Accessport however the K&N Intake system will need to be custom calibrated. We offer OTS maps for our SF Intake or the AEM Cold Air Intake for the 2013 WRX. If you were to swap your intake out for one of those two, you would be able to use our free Off The Shelf maps!
Marshall@COBB
When does the Stage 2 COBB SF intake maps coming out? Also, will there be a Stage 3 maps soon?
We will likely not be offering a Stage2+SF map for the 2015 STI. Recent testing has shown that the factory fuel system can deliver enough fuel for an upgraded downpipe OR intake, but not both. Keep an eye out for some updates towards the end of February covering fuel upgrades and our Stage 3 Power Package!
Marshall@COBB
Any update on the Cobb Air Box for the 2015 STi? Will there be an updated OTS map for the intake with a box?
Hey Scott, we’re due to announce the Airbox as part of this month’s hard-parts release. Keep an eye out for that next week!
Marshall@COBB
Are we still looking to see that air box this week? Time is running out for this week pretty quick!
They literally JUST showed up. Been dealing with weather delays for the past week. They may not make it out today, but should be announced first thing next week!
Marshall@COBB
Are you guys still planning on the staged package that includes air intake, injectors, pump, & tune for 2015 sti? If so, is this going to be offered soon? Thanks
We are. We’re finalizing some fuel pump testing here over the next few weeks and should have that package released by the end of March!
Marshall@COBB
Are you going to release an OTS map for an AEM intake on a 2015 sti anytime soon? If now what tune should I run?
We do not currently have any plans to release an OTS map for the AEM intake. It’s possible that will change, however currently I would have to recommend a custom tune for that setup. If you’re comfortable in doing so, the MAF calibration data from one of our +AEM maps for the 08-14 STI could be applied to our one of our current 2015 OTS maps and get you close.
Marshall@COBB
Will there be a map release for cvt 15 wrx with the aem cold air intake.?
We do not currently have any plans to support the AEM Intake for the 2015 WRX. We currently have support for the Mishimoto intake and will be releasing our SF Intake and complimentary maps soon!
Marshall@COBB
Marshall u recently hook me up with a 1000 cc injection cobb intake and air box and 3 port boost controller I bought 2 v3 accessport and 1 for 2006 sti plus a down pipe and I total my 2015 sti i wanna buy another 2015 sti but the tow company stolen my accessport and it not uninstall coz the car can’t turn on can u just keep an eye if anyone from maui Hawaii try to send a uninstall accessport thank u serial no# SUB400732
Terribly sorry to hear about that! We’ll add that serial number to the stolen list, it will not be able to be reprogrammed.
Marshall@COBB
Hello Marshall, I currently have the AP for the 2015 sti and cobb intake installed with proper maps in California. I’m currently in the market for a full turbo back exhaust and was wondering if I were to install the Tomei extreme ti turboback, would the AP map be able to support this or would a pro tune need to be done. Probably a dumb question but I admit I’m still new to the Subaru world. I really like the sound of the tomei exhaust. Or maybe is there another option like say, cobb down pipe to mid pipe and just the tomei exhaust? Thanks for any info
Hey Frank, I currently cannot recommend installing a turboback exhaust along with the SF Intake. The 2015 STI does make a bit more power than previous years, so the factory fuel system is not capable of supporting an intake+exhaust setup. With that said, leaving the factory downpipe in place and only replacing the catback section would be just fine.
Check out this blog post for a complete explanation : http://blogs.cobbtuning.com/2015/02/17/2015-sti-development-staged-power-package-evaluation/
Hope that helps!
Marshall@COBB
Thank u Marshall can u hook me up with my 4th v3 accessport for my brand new 2015 sti
Give our Customer Service Team a call (1-866-922-3059), I’m sure we can work something out for you!
Marshall@COBB
Marshall, it’s now nearing Oct ’15 and I wanted to check the status of supporting any other intakes other than your own via OTS tunes for the ’15+ STI’s??
Hey Nate, thanks for following up! We do not currently have plans to offer support for additional intakes. Any of our Protuners would definitely be able to provide a custom map or you can utilize our free Accesstuner Race software if you’re comfortable creating your own MAF calibration.
Marshall@COBB