2015+ Subaru WRX (FA20DIT) - Full Op-Ed (CSTuned)
2015+ Subaru WRX (FA20DIT) - Full Op-Ed (CSTuned)
Hello and welcome to my Op-Ed on the 2015+ Subaru WRX! This editorial plans to encompass all of the information you will need to make informed decisions regarding the best upgrade path for your vehicle.
In this editorial, I will be discussing my background with the FA20DIT platform as it relates to part testing and ECU calibration as well as covering why the information in this article may be of use to you! I will also be giving an in-depth overview of the following topics: Intakes, Bypass Valves, Turbo Inlets, Electronic Boost Control Solenoids, Turbochargers, Intercoolers / Charge Pipes, Intake Manifolds, Tumble Generator Valves, Engine Builds, Downpipes, Cat-Back Exhausts / Muffler Deletes, Air-Oil Separators, Powertrain / Drivetrain Bracing, Suspension Upgrades, Braking Upgrades, Transmission Swaps, Clutch Upgrades, Ethanol Sensors, Low / High Pressure Fuel Pumps, and Alternative Fuels (Methanol / Ethanol). This overview will consider the purpose of each component, how to account for it in a calibration file, as well as what specific brands I recommend.
Disclaimer
The statements made in the article below are subjective and based on my knowledge and experience gained from working with the VA WRX platform. Please refer to your preferred tuner, or a trusted vendor, for recommendations on your specific set up.
Intentions
This Op-Ed is intended to help the user better understand how certain modifications affect the engine and performance, what tuning changes are necessary to account for these modifications, and what brand(s) I recommend for each modification category. This is NOT intended to be a tuning guide. I am NOT an expert in ANY category that will be discussed.
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My Background
VA WRX (FA20DIT) Platform
I have owned a 2016 Subaru WRX for almost 4 years now. In that time, I have done many modifications, tested different brands and components, and spent quite a few hours on the track. My experience in setups and tuning is currently specialized within this specific platform. However, I do hope to branch out to other platforms in the future.
Part Testing
Ever since I began ownership of my 2016 WRX, modifications have been a way of life. Whether it’s increasing airflow or decreasing knock, the aftermarket industry has played a big role in shaping my vehicle into what it is today. Brands like COBB, IAG, and IBR to name a few, have made giant leaps on the VA WRX platform by providing not only performance parts, but the means to control the ECU (Engine Control Unit) calibration as well. Since I started tuning, I have compared and contrasted many different parts on my own vehicle in an effort to provide insight into what parts may be best for any given setup and what parts could have their cost better spent elsewhere.
ECU Calibration
At the start of 2020, I began studying to become a tuner. My platform of choice was the 2015+ Subaru WRX (FA20DIT). I was inspired to choose this platform from legendary Subaru tuners such as Jr, Botti, Ambot, Adkins, Bains, Shinji, and many others. Since I already owned the vehicle, it was a great place for me to start.
Through COBB’s software support and HP Academy, I learned the basics of ECU calibration and how to apply them to my own vehicle. After many revisions and countless hours of testing, I had my engine performing as close to optimally as I could. From there, I reached out to friends on the same platform and began tuning their cars and I immediately fell in love with the idea of tuning in general. Coming from an engineering background, I had a good fundamental understanding of how an internal combustion engine operated and what was required to make it function optimally.
From friend’s cars, I branched out to Facebook forums and other mediums with the intention of making quality calibrations attainable for the masses. This included not only making tuning affordable, but also being transparent and allowing customers to learn about the changes that are being made to their vehicles instead of keeping them in the dark. Knowledge is power and spreading that knowledge is the main goal behind this Op-Ed and my tuning career in general. The support I have gotten from the community, as a whole, has been outstanding and I am excited every day for the ability to be able to share my passion with others.
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Modifications and Preferred Brands
Intakes
As the primary point entry for air into your engine, an intake is very important. An intake can either encourage healthy airflow, or restrict it. A good intake will also protect against heat and water as the vehicle is driven through a variety of different conditions. The OEM intake is sufficient for most common builds. However, people prefer the turbo noise to not be muffled. Hence, an intake is one of the most common modifications out there.
Some key considerations to make when sourcing an intake are as follows. What is the pipe diameter? Pipe diameter will either encourage or restrict air flow depending on pipe size and bend geometry. Is the MAF (Mass Air Flow) sensor housing different? The MAF housing will affect how air is calculated as it passes the sensor. How does the intake control temperature and protect against hydro-lock? An intake with a heat shield is the best way to protect usable air from radiant heat. It also can protect against water as it splashes up into the engine bay.
Tuning changes for an aftermarket intake generally revolve around properly scaling the MAF sensor to ensure that the proper amount of air is being accounted for as it enters the engine. If this sensor is improperly calibrated, the ECU will compensate by adding or removing fuel, as necessary, as determined by the measured AFR (Air Fuel Ratio) at the wideband O2 (Oxygen) sensor during closed-loop operation. Not accounting for an intake during tuning can result in elevated fuel trims and generally erratic fueling which can lead to bigger issues down the line.
For intakes, I would recommend either the COBB Big SF or GrimmSpeed StealthBox units. I have had great results testing with both of these units. The COBB unit is a bit more robust. However, the GrimmSpeed unit has a better fit and finish, in my opinion. The GrimmSpeed unit also has a clever design that eliminates any guesswork when placing the air filter. This means that there is more consistency from one setup to the next.
Subaru Big SF Intake System WRX 2015-2020
GrimmSpeed StealthBox Cold Air Intake Black - 15-20 WRX
Bypass Valves
A bypass valve is important, especially for the FA20DIT which utilizes a fully recirculating air flow path to accurately account for all air in the system. Instead of venting excess air into the atmosphere like a traditional BOV (Blow Off Valve), the BPV (Bypass Valve) will recirculate excess air back into the intake tract. This allows for the correct amount of air in the system to be preserved, especially during transient operating conditions. The OEM BPV is sufficient for most applications. However, it is plastic and prone to failure over time.
Some key considerations to make when sourcing a BPV are as follows. Does the unit recirculate 100% of the excess air? If it does not, then I would look at a unit that does. My experience with VTA (Vent To Atmosphere) setups is minimal. However, from a conceptual standpoint, if air is accounted for and then lost, the engine will be expecting more air than it will receive. This will cause a rich condition and is not optimal for most situations. Does the unit leak? A BPV that leaks can cause a wide variety of operating concerns as the vacuum in the system is no longer preserved.
Installing a fully recirculating BPV requires no general tuning changes. However, installing a VTA unit may require an adjustment to the VE (Volumetric Efficiency) table(s). Nevertheless, it is best to discuss the application of a hybrid or full VTA charge pressure release system with your preferred tuner.
For BPVs, I would recommend the COBB LF unit. The Boomba unit is adequate as well. However, I’ve heard more horror stories about the Boomba unit vs. the COBB unit. I personally run the Boomba unit and have had no issues thus far.
Boomba Racing Bypass Valve - 15-20 WRX / 14+ Forester
Turbo Inlets
A turbo inlet is a critical component that allows air to transfer smoothly from the intake to the turbo. By design, the unit should flow as freely as possible and provide an ample seal between the components it connects. For this reason, some flexibility and resilience is important. The OEM inlet is sufficient for most applications. However, it is plastic and prone to failure over time. It is also designed to lightly tumble air as it enters the compressor housing of the turbo. This may or may not be desirable depending on your specific situation.
Some key considerations to make when sourcing a turbo inlet are as follows. Does the unit flow air laminarly? Laminar (non-turbulent) flow will be more efficient and predictable overall. Does the unit provide an ample seal from the intake to the turbo? If not, then a vacuum leak will be introduced. Is the unit resilient? If not, it may fail over time due to heat and stress.
Installing a turbo inlet requires no general tuning changes. However, it is best to share a post-install log with your preferred tuner so that any potential vacuum leaks can be identified and corrected.
For turbo inlets, I would recommend the Perrin unit. There’s not much competition on the market at the moment and the wireframe/silicone design is perfect for most setups.
Perrin Turbo Inlet Hose w/ Nozzles - 15-20 WRX
Electronic Boost Control Solenoids
An EBCS (Electronic Boost Control Solenoid) is a crucial tuning component as it allows the boost pressure to be accurately controlled. This prevents surges, spikes, and irregularities while also facilitating more consistency across the board. A well set up boost control system can result in more horsepower and better drivability overall. The FA20DIT is equipped with a 2-Port EBCS from the factory. However, the aftermarket 3-Port options typically perform much better.
In order to understand how an EBCS works, we need to understand how the Subaru boost control system functions. Programmed into the ECU is a P/I (Proportional / Integral) gain system which operates in closed loop at all times. This means that there is a constant comparison between the target boost and the manifold relative pressure or boost pressure. This comparison will always result in an error. This error is calculated via the following equation: [Boost Error] = [Target Boost] - [Manifold Relative Pressure]. This means that a positive boost error value indicates under-boosting and a negative value indicates over-boosting. The ECU will take this value and apply a WGDC (Wastegate Duty Cycle) multiplier in order to fine tune the boost control system on the fly - in the same way that the ECU will use an AFR (Air Fuel Ratio) error to adjust fueling in closed loop operation. Setting up this system to perform effectively is as simple as understanding how a P/I system is optimized. Minimizing overshoot and downtime are the two key aspects to enhancing the performance of any boost control system. Coincidently, these are the two main reasons why an EBCS is such a powerful tool, since it allows the user greater control over those two functions.
Some key considerations to make when sourcing an EBCS are as follows. Does the unit provide better boost control? In most cases, yes it will. Do I need the unit for my specific setup? This really depends on your goals for the vehicle. Like with most things, it’s a worthwhile discussion to have with your preferred tuner. That being said, I will ALWAYS recommend an EBCS on any setup. It's simply so much value added for being relatively inexpensive and simple to install.
Tuning changes for an aftermarket EBCS generally revolve around updating the solenoid frequency based on the manufacturer’s recommendation as well as adjusting wastegate duty and P/I gain as necessary. Since the OEM EBCS is set to run at 10 Hz, other units may require a higher or lower frequency depending on what the manufacturer recommends.
For an EBCS, I would recommend either the COBB or GrimmSpeed 3-Port units. Both of these units provide significantly better boost control and more consistency overall. This would be one of my top recommended modifications on any VA WRX build sheet.
Subaru 3-Port Boost Control Solenoid (BCS) WRX 2015-2020
GrimmSpeed 3-Port EBCS Boost Controller - 15-20 WRX/FA20
Turbochargers
A turbocharger is the focal point of the FA20DIT. It uses exhaust flow to drive a turbine. That turbine is connected to a compressor. That compressor creates a vacuum that pulls air from the intake into the engine. More air allows for more fuel and more power. The factory turbocharger is designed for low to mid range performance and does suffer at the top end as a result. However, for most builds under 400 hp (horsepower), the OEM turbocharger will perform well enough since most mild builds will be limited by knock, not airflow.
Some key considerations to make when sourcing a turbocharger are as follows. Does the unit fit stock location? Depending on your build, this may or may not be ideal. What are the flow characteristics of the turbocharger? This will change how and when your engine produces torque. There are many other considerations to make when sourcing a turbocharger for your engine. However, it is always best to discuss your goals with your preferred tuner and decide, from there, which turbocharger setup is best for your specific situation.
In general, tuning on an aftermarket turbocharger is relatively similar to tuning on a stock unit. There are simply different targets to reach at different points in the torque curve. Typically, the larger the turbo, the more air it can supply over a period of time. The added rotational inertia of a larger compressor also means more lag and more resistance to deceleration. Fuel delivery may need to be augmented to support the extra airflow and other engine components may need to be upgraded to facilitate healthy engine operation under more stressful conditions.
For a turbocharger, I would recommend the SoCal v3 upgrade or an FP Blue Series unit. Both of these options fit stock location and will provide enough flow to reach the power capabilities of most OEM internal powertrain components.
(V3) FA WRX – SoCal Porting and Polishing
Forced Performance Blue Turbocharger - 15-20 WRX
Intercoolers / Charge Pipes
An intercooler is fundamental to any forced induction setup. It serves the purpose of cooling incoming charge as it makes its way from the turbo to the intake manifold. For most applications, an air to air intercooler will be used wherein cool atmospheric crossflow extracts heat from the charged transverse flow produced by the turbo. Cold charge is a high priority for turbo applications as it helps increase the density of the inflow and reduces the combustion temperature and chance of knock. The charge pipe serves as the medium through which air flows from the turbo to the intercooler. The OEM TMIC (Top Mount Intercooler) works well for its daily driving intention. However, there is a major drawback. Back to back pulls and heavy abuse quickly produce heat soak which can lead to detonation. As a result, a richer AFR and a well tapered boost curve are two examples of ways that tuners can help combat that detonation.
Some key considerations to make when sourcing an intercooler and charge pipe are as follows. Top Mount vs Front Mount? A TMIC will usually do the job for most applications. However, a FMIC (Front Mount Intercooler) will offer a few additional benefits: Increased surface area and volume, more consistent charge temps, heavy abuse protection, and the ability to avoid engine bay heat soak, to name a few. Will the charge pipe and TMIC fit together? Ideally, a charge pipe and TMIC should be sourced together and from the same manufacturer to ensure optimal fitment. An intercooler is the epitome of “you get what you pay for” seeing as some cheaper intercoolers perform only slightly better than the factory unit. Be wary of this and spend your money wisely.
Installing an intercooler and/or charge pipe requires no general tuning changes. However, the benefits come from being able to lean out the AFR and increase the boost. That being said, if you’d like to experience less heat soak and the general benefits of a more robust cooling system, you can simply bolt it on and go. However, it may be smart to consult with your preferred tuner to ensure than no vacuum leaks have developed during the installation process.
For an intercooler and charge pipe combination, I'd recommend the COBB or GrimmSpeed TMIC options. They have been proven to be consistent and robust units, perfect for the daily or spirited driver. For track day enthusiasts, I’d recommend either the GrimmSpeed or ETS FMIC options. As always, the larger the core, the more effective the ambient airflow will be, but there will also be more volume for the turbocharger to fill. This is why a massively oversized intercooler can actually be a detriment to a moderate build. Whatever path you follow, just be sure to protect the fins from road debris and other potential damages.
Subaru WRX Top Mount Intercooler
GrimmSpeed Top Mount Intercooler Kit - 15-20 WRX
GrimmSpeed Front Mount Intercooler Kit Silver Core Black Piping - 15-20 WRX
ETS Front Mount Intercooler Core - 15-20 WRX
Intake Manifolds
A cleverly designed intake manifold can make or break airflow to the engine. It serves as the distribution hub that sends incoming charge where it needs to go. In some applications, an intake manifold can also allow the user an opportunity to exceed factory fueling limitations via secondary fuel injection. For most applications, the OEM intake manifold will meet airflow and distribution needs. However, there can be some dramatic benefits to upgrading to a more stout unit.
Some key considerations to make when sourcing an intake manifold are as follows. Do my power goals require one? In most cases, no. However, on bigger builds, they may provide better flow characteristics. Do I need to introduce port injection? This is the main reason why people opt for an upgraded intake manifold. Since there is not much support for DI (Direct Injection) component upgrades, PI (Port Injection) seems to be a good solution for some situations. Breaching fueling limits is something best discussed with your preferred tuner. The OEM FA20DIT fuel system is capable of around 450 hp before port injection should be considered.
I have not worked with any aftermarket intake manifolds at this time so I cannot speak on what tuning changes are required to run them. For situations like this, please contact your preferred tuner.
For an intake manifold, I would either recommend the IBR BRZ or IBR Ultimate Intake Manifolds. Both of these options can help achieve the power goals you most likely have. Keep in mind that different cold-side intercooler piping may need to be sourced depending on the specific application.
IBR / Subaru OEM BRZ Manifold/Bolt-On Kit Red - 15-20 WRX
IBR Intake Manifold - 15-20 WRX
Tumble Generator Valves
TGVs (Tumble Generator Valves) are emissions components that serve the purpose of tumbling the charge as it enters the cylinders. This helps facilitate a more complete combustion as well as aiding in cold start conditions. However, these systems also cause a bottleneck in the intake tract and do disturb airflow, especially at high load. They also activate under certain cruising conditions which can lead to periodic cruise and tip-in knock and other non-ideal operating conditions. Ultimately, elimination of this system is critical to extract the most performance from your engine. However, do understand that there will be some drawbacks to removing this system, especially when it comes to post-start fuel enrichment and achieving complete combustion under certain circumstances.
Some key considerations to make when sourcing a TGV housing kit is as follows. Will I pass emissions? Depending on your area and laws, this may be something to consider. I recommend looking into local emissions guidelines before making the choice to remove your TGV system. Uppers, lowers, or both? I am a big fan of removing the upper and lower TGV housings and replacing them with a full TGV housing kit. This will yield the best benefits despite costing a bit more than a traditional upper TGV housing kit. A full kit will also contain less points of potential seal failure which can cause a vacuum leak. If installing a full TGV housing kit, I recommend removing the intake tract dividers that fit below the lower TGV housing before reassembling everything. However, removal of these dividers have not proved to provide any additional benefits or drawbacks.
Removing your TGV system requires a few tuning changes. For certain applications, some fault codes may need to be suppressed in the calibration file and the TGV compensations must be modified in order to facilitate optimal engine operation within the newly defined parameters.
For a TGV housing kit, I’d recommend the IAG Full TGV Housing Kit. This replaces both the upper and lower TGV housings with port matched CNC runners for optimal flow. The IBR kit is fantastic as well, despite not being port matched and also being casted instead of machined. Once again, try to purchase it as a bundle with other modifications to save some money.
Built Blocks
For bigger builds, the power capacity of the stock block and internals may be reached. In this case, an upgraded internal setup will be required. Torque is typically capped at 350-375 WTQ (Wheel Torque) in order to preserve the integrity of the connecting rods. OEM FA20DIT rods are especially thin to help reduce oscillating mass and increase engine efficiency. As a result, they are the weak point in many cases. An engine build can also help increase the durability of other internal components, such as the pistons or the crankshaft, without sacrificing engine cooling and the amount of power than can safely be made. An upgraded valvetrain may also be a worthwhile consideration for some applications. However, we will not be discussing that topic in this editorial.
The only key consideration to make when sourcing a built block is as follows. What are the power goals? You should source your internals or built block packages based on power goals. Certain packages will be rated for certain applications. However, It’s always a good idea to over-build as it can save you a lot of money in the long run.
I have not worked with any aftermarket built blocks at this time so I cannot speak on what tuning changes are required to run them. For situations like this, please contact your preferred tuner.
For an engine build, I’d recommend browsing the offerings from IAG and seeing which package best meets your requirements. I would advise against replacing internals only. Unless you really know what you’re doing and have the tools to support the process, leave the guesswork and assembly out of the equation. You’ll thank yourself later.
Downpipes
As the primary exit point of air from your turbo, the downpipe is tasked with diverting exhaust flow away from the turbo as quickly and efficiently as possible. Air can only enter the engine as quickly as it can exit it. For this reason, a free-flowing downpipe is integral to optimal engine performance. However, the downpipe is also a critical emissions component, as it houses the catalyst. The catalyst uses a combination of platinum and rhodium to facilitate oxidation to remove nitrogen atoms from nitrogen-oxide molecules in order to reduce harmful emissions. The OEM downpipe houses one catalyst and one resonator but features less than optimal geometry.
The only key consideration to make when sourcing a downpipe is as follows. Will I pass emissions? Depending on your county and laws, this may be something to consider. I recommend looking into how your area conducts emission testing before making the choice to modify your catalyst.
Upgrading the downpipe does require a few tuning changes. For certain applications, some fault codes may need to be suppressed in the calibration file and the wastegate duty will need to be re-calibrated in order to account for the loss in back pressure.
For a downpipe, I’d recommend either the COBB or GrimmSpeed catted units. These brands offer superior build quality and excellent flow characteristics. This is especially apparent in the GrimmSpeed unit which is made in the USA and boasts a superior fit and finish. The catalysts on these units are high-flow, yet still very efficient at converting pollutants.
GrimmSpeed Catted J-Pipe 6MT - 15-20 WRX
Cat-Back Exhausts / Muffler Deletes
Post catalyst exhaust components simply alter the sound characteristics of the exhaust as well as remove excess weight. However, a more free-flowing midpipe my net some positive throttle response as well. The OEM cat-back exhaust includes a non-resonated midpipe and two mufflers.
Since post catalyst components do not have a noticeable effect on performance, the only considerations would be your own audible and visual approval as well as weight savings. However, it doesn’t hurt to stick with a name brand so as to preserve build quality, material choice, and fitment.
Installing a CBE (Cat-Back Exhaust) or muffler deletes requires no general tuning changes.
For post catalyst exhaust components, I’d recommend whatever fits your budget, look, sound preference, and desired weight. For dual exit, I prefer the Invidia Q300 or R400 depending on how aggressive of a sound you’re looking to achieve. For single exit, I prefer any system from Carven. Carven is made in the USA and offers superior weld quality and fitment when compared to other brands.
Air-Oil Separators
An AOS (Air-Oil Separator) or catch cans serve the purpose of keeping blow-by and oil out of the intake tract and engine. As a result, installing one can help prevent carbon buildup, exhaust smoke, and detonation. It’s one of the most helpful supporting modifications out there for the FA20DIT and highly recommended by tuners and engine builders alike.
Some key considerations to make when sourcing an AOS are as follows. Is a maintenance free experience important? Then an AOS is preferred over catch cans. What are the power goals? That will determine what type of AOS to install.
For any type of recirculating AOS, there will be no tune required. This is because the factory PCV (Positive Crankcase Ventilation) functionality is retained. For any VTA (Vent To Atmosphere) AOS, tuning changes may be required to account for changes made to the PCV system. In either case, it is best to discuss the available options with your preferred tuner.
For an AOS, I’d recommend the IAG street series unit for any engine build below 600 hp. For anything over 600 hp, I’d recommend the IAG competition series unit. This is per IAG and not based on personal preference. For catch cans, I’d recommend the Radium unit. It seems to be the most consistent and the most effective overall at keeping oil and vapors out of the intake and engine.
IAG V3 Street Series Air Oil Separator Black - 15-20 WRX
IAG V3 Competition Series Air Oil Separator Black - 15-20 WRX
Powertrain / Drivetrain Bracing
When adding power, it’s always important to understand how the chassis will respond. Most factory support components were designed with specific torque thresholds in mind. When these thresholds are exceeded, the added stress can cause OEM components to fail either abruptly, or over time. Since every build is different, I recommend contacting your preferred tuner when deciding what supporting mods are best for your specific situation.
Some key considerations to make when sourcing aftermarket bracing are as follows. What are the power goals? The more power you make, the more reinforcement will be required. How will the car be driven? Daily drivers will not require the same supporting modifications as race cars will. Extra bracing will typically make the car more noisy and less comfortable, especially on long trips. To better understand what components are best for you, contact your preferred tuner or even a trusted vendor.
For chassis bracing, I’d recommend the following upgrades depending on your situation: Perrin Pitch Stop Mount and Pitch Stop Brace Kit. These two modifications can help redistribute the bending moment between the engine and the transmission to other parts of the vehicle’s frame. This can help prevent components from being damaged due to elevated levels of torque stress. The Pitch Stop Brace Kit also comes with a stainless steel clutch line that can help increase positivity in both clutch feel and engagement.
Perrin Pitch Stop Mount Black - WRX/STI
Perrin Pitch Stop Brace - 15-20 WRX/STI
Suspension Upgrades
Suspension is what will keep your tires in contact with the road. As a very complex subject, suspension setup will completely rely on your vehicle’s intended use, your preferences, your driving style, and many other factors. A good suspension setup is well thought out and proven under certain conditions. As with most things, functionality is fundamental and looks should come second. Your safety and your vehicle's cornering performance should ALWAYS be a top priority when upgrading or changing suspension components.
Some key considerations to make when sourcing suspension are as follows. How will the car be driven? Daily drivers and race cars will require vastly different setups. Depending on your intentions, different combinations of spring rates, ride heights, and dampening may be necessary. Do I require on the fly adjustability? If so, air suspension may be your best bet. Air ride cannot match the functionality of a well dialed-in coilover setup. However, for certain applications, the versatility of air ride is simply unmatched. Can I simply get lowering springs and call it a day? Many people have seen success with a lowering spring setup. However, I would advise against it. OEM struts were designed to work optimally with OEM springs. When you change those springs out, you not only put the OEM struts outside of their intended dampening zone, but you also put transfer stress and impulses through the struts during operation. This will typically lead to poor suspension performance and premature failure of the struts. Nevertheless, if you pair a lowering spring with an aftermarket strut that was designed to dampen optimally with said spring, this could potentially be a more cost effective solution for you, depending on the application.
For a coilover setup, I’d recommend something from Fortune Auto. They have been in the business for a very long time and only release a new product once it has been extensively simulated and road tested. They are also the pinnacle of price for performance and are widely known for being one of the best “bang for your buck” options out there. For air suspension, my knowledge is fairly limited. In either case, It is best to contact a suspension or fitment specialist regarding what setup is best for your situation.
Braking Upgrades
After adding all that power, you’ll need some extra help slowing down. The factory brakes are sufficient for daily driving. However, under heavy or extended use, there are a few major concerns. The brake pads will fade, the rotors will warp, the lines will expand, and the fluid will boil. All of these things can lead to a substantial decrease in braking performance and a potentially dangerous situation.
The only key consideration to make when sourcing braking components is as follows. How will the car be driven? Daily drivers and race cars will require vastly different setups. Depending on your intentions, different combinations of pads, rotors, lines, and fluid may be necessary. The level of heat capacity and wear characteristics will also come into play when determining what upgrades are best for your specific situation. Braking setups vary across different racing disciplines from Autocross to Time Attack and everything in between. In most cases, it is best to consult with someone who has on-track experience before making any expensive brake purchases.
Do not be fooled by fancy designs in brake rotors. Drilled or slotted rotors may look nice. However, they may not be the best option in some cases. While slotted rotors can aid in the disbursement of brake dust, drilled rotors offer few inherent benefits over well designed blank rotors. At the same time, most track day enthusiasts often opt for blank rotors as they are the cheapest to replace when the time comes. Take all of these factors into consideration and contact a trusted vendor to identify what rotor setup is best for your specific situation.
As far as brake pads go, there are plenty of considerations to make. Different brake pads will produce different amounts of stopping power, different noise and dust levels, and different longevity characteristics. Too aggressive of a pad on a street car will create excess dust and noise. Too docile of a pad on a track car will result in brake fade or accelerated wear. At the same time, pads should be sourced with rotors in mind. Too aggressive of a pad on a street rotor can lead to the rotors warping or delaminating. This directly effects not only the performance of your braking system, but the longevity of the components as well.
Regarding brake lines and fluid, traditional rubber lines will expand as pressure and heat build in the braking system. This can result is negative pedal feel and a decrease in maximum braking pressure. At the same time, boiling brake fluid reduces the fluid’s ability to remain incompressible and extract additional heat. For these reasons, selecting a fluid that can resist boiling and lines that can resist volumetric expansion are critical in maximizing your braking performance. This is especially important when it comes to high stress situations, such as track time and autocross.
For braking setups, I’d recommend Hawk Pads, DBA Rotors, StopTech Lines, and ATE-200 Fluid, or perhaps a Big Brake Kit from your preferred manufacturer. Since brakes function by transforming kinetic energy into heat via friction, heat extraction should may also need to be considered. This can be addressed via brake ducting or other methods of increasing the flow of clean air over the braking surface(s). In any case, It is best to contact a braking specialist, or a trusted vendor, regarding what setup is best for your specific application.
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StopTech Stainless Steel Brake Lines - Front - 08-20 WRX/STI
StopTech Stainless Steel Brake Lines - Rear - 08-20 WRX
ATE 706202 Original TYP 200 Racing Quality DOT 4 Brake Fluid - 1 Liter
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Subaru STI 6-Piston/2-Piston Brembo Brake Kit
Transmission Swaps
The transmission is the essential assembly that transfers power from the engine to the wheels. The OEM split-case 6-speed cable-style transmission in the VA WRX is perfectly capable in most cases. However, under heavy abuse or high torque applications, problems may arise and components may fail prematurely.
When debating a transmission upgrade, bear in mind the torque goals. Some transmissions aren’t designed to handle well over factory power levels. Some transmissions aren’t meant to handle aggressive driving at factory power levels. All of these factors come into play when deciding what transmission is best for your specific situation.
In any case, if a transmission upgrade becomes a necessity, the best option is usually to source a 6-speed linkage-style drivetrain swap from a VA STi. Certain gears in the STi transmission are considerably thicker than their split-case counterparts; this aids both in power delivery and longevity. Seeing as most components are drop-in ready, there is typically no better way to ensure power is transferred safely to the ground.
Clutch Upgrades
The clutch is a critical power transmission component as it regulates the torque delivery to the transmission. In most situations, the OEM clutch is perfectly sufficient. However, if the vehicle sees frequent launches, heavy abuse, or an abundance of extra torque, the factory clutch may begin to slip.
As a tuner, I have seen many clutches fail when torque rises well above factory specifications. It’s not as much a matter of if, but a matter of when. I always recommend installing a clutch that can handle 25% more torque than what it will be subjected to. This will ensure a sufficient factor of safety on all torque transfer components.
With so many solid clutch options out there, it’s really best to contact your preferred tuner, or a trusted vendor, when sourcing an aftermarket clutch, flywheel, or combination of the two. Just make sure that the components are rated above the amount of torque you plan on producing. That way, you can ensure longevity of the assembly in all circumstances and situations.
Ethanol Sensors
The ethanol sensor is the component that measures ethanol content in the fuel system. It is responsible for ensuring that the ECU understands ethanol content in order to properly adjust the flex fuel calibration on the fly. There is currently no factory option for an ethanol sensor. However, there are many aftermarket options available.
An ethanol sensor works by allowing the fuel to flow through the gaps between the inner and outer electrodes as an AC voltage is applied to the electrodes. The relative permittivity of the fuel changes with the ethanol content, which leads to a change in the capacity accordingly. As the capacitance increases with increasing ethanol content, the oscillation frequency in the system will decrease and vice versa.
The analog frequency output is tied to a microprocessor which determines the capacitance by working backwards from the measured frequency. Due to the correlation between ethanol’s permittivity and the fluid’s temperature, the microprocessor corrects the capacitance for temperature variations in the fuel according to the output from an NTC (Negative Temperature Coefficient) thermistor. In addition, errors caused by the different conductivities of gasoline and ethanol are corrected.
The frequency of the single-wire output of the microprocessor to the ECM indicates the percentage of ethanol in the fuel. If required by the OEM the pulse width of the signal will indicate the fuel temperature. The ECM adjusts the injection according to the blend of the fuel, which leads to a stoichiometric combustion.
Installing an ethanol sensor does require a few tuning changes. The sensor must be activated and properly calibrated before it can be used and trusted for accurate readings.
For an ethanol sensor, I’d recommend the Flex Fuel Kit from COBB.
Subaru Flex Fuel Ethanol Sensor Kit - WRX 2015-2020
Low Pressure Fuel Pumps
The LPFP (Low Pressure Fuel Pump) is responsible for drawing fuel from the fuel tank towards the engine. The factory LPFP does not support ethanol usage in saturations greater than 10%.
A LPFP works by first drawing fuel into the pump through an inlet tube and filter system. The fuel then exits the pump through a one-way check valve which maintains residual pressure in the system when the pump is not running, and is pushed toward the engine through the fuel line and filter. The fuel filter traps any rust, dirt or other solid contaminants that may have passed through the pump. Fuel then flows to towards the engine.
Installing an aftermarket LPFP requires no general tuning changes.
For a LPFP, I’d recommend the AEM unit in conjunction with the DW Installation Kit.
AEM 340LPH Fuel Pump (E85 Compatible) with DW Install Kit - 15-20 WRX
High Pressure Fuel Pumps
The HPFP (High Pressure Fuel Pump) is responsible for pressurizing the fuel and forcing it into the engine. The factory HPFP does not support ethanol usage in saturations above 60%. Even with ethanol saturations below 60%, it is always advised to cycle a full tank of pump fuel for every two tanks of the preferred ethanol blend. This will increase the lifespan of the HPFP.
High-Pressure fuel pumps are mechanical and are typically driven by a camshaft. A lobe on the camshaft pushes a follower or roller that moves a piston. The piston in the pump has two cycles, suction and compression. The solenoid on the side of the pump controls how much fuel is compressed during the compression stroke. During the suction cycle, the solenoid will allow fuel from the low-pressure side of the fuel system to enter the pump. As the piston starts to travel upwards, the solenoid will remain open. The fuel is then pushed into the low-pressure side of the fuel system when the solenoid is open. When the solenoid is closed, the low-pressure and high-pressure sides of the fuel system are isolated.
If there is a small load on the engine, the solenoid will remain open longer and a smaller amount volume of fuel is compressed. If there is a large load on the engine, the solenoid will close sooner and a higher volume of fuel will be compressed. The length of time that the solenoid remains open will determine how much fuel reaches the injectors.
I have not worked with any aftermarket HPFP units at this time so I cannot speak on what tuning changes are required to run them. For situations like this, please contact your preferred tuner.
For a HPFP, I’d recommend the Nostrum unit. I would recommend this unit to anyone interested in utilizing full E85 or 85+% ethanol blends in their vehicle.
Nostrum High Pressure Fuel Pump HPFP Kit w/ Free Shirt - 15-20 WRX
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Alternative Fuels
Methanol
Methanol injection is the process through which an atomized mixture of water and methanol fuel is injected into your engine’s intake tract. This offers multiple benefits including, but not limited to: increasing octane, reducing EGT (Exhaust Gas Temperature), and suppressing detonation.
Methanol is typically introduced immediately before the throttle body by means of an injector. The injector is controlled via a control unit that has a built-in pressure sensor and multiple controls. The user typically has control over what parameters must be met in order for the injector to activate and deactivate. On most systems, the amount of injected methanol blend is controlled by a jet device that goes in the injector nozzle, and then into the intake system.
While the benefits of methanol injection are substantial, I will not be discussing methanol further because my experience with it is extremely limited. For additional questions about methanol injection, please contact your preferred tuner.
15+ WRX Water / Meth Injection
Ethanol
Ethanol is derived from corn whereas gasoline is derived from petroleum. In fact, ethanol was originally mixed with gasoline in an effort to make the mixture non-potable! Ethanol contains less energy per unit than gasoline does. This results in a reduction in fuel economy. It also doesn't provide the same lubricating qualities that gasoline does which results in excess wear on fuel system components such as the high and low pressure fuel pumps. However, these downsides are heavily outweighed by the many upsides of running ethanol.
Octane Boost: Ethanol provides a sufficient boost in octane when mixed with gasoline. The process of mixing ethanol and gasoline together is called blending. Typically, pump gasoline sits somewhere between 0% and 10% ethanol content. This solely depends on the provider and distributor. Pump E85 typically sits between 51% and 83% ethanol content. This depends on the provider, distributor, geography, and season. Depending on specific content and mixing ratios, one can theoretically achieve any ethanol content between 0% and 83% depending on the factors mentioned above. As this percentage increases, so strengthens the pros and cons of ethanol in your vehicle. It is also worthwhile to mention that purer forms of ethanol (>83%) can be sourced as well although it is typically not sold at public fuel stations.
Combustion Temperature: Because ethanol has a lower BTU (British Thermal Units) value than gasoline, it actually burns slightly colder than gasoline does. This adds more knock resistance and fortifies the benefits of something like a larger intercooler. For this reason, ethanol is a very enticing fuel for any vehicle that sees heavy abuse, such as a race car.
Flex Fuel: Another benefit of ethanol is the ability to program a flex fuel setup on your vehicle. Flex fuel is the ECU’s ability to determine and adjust a set of parameters based on a measured ethanol content. It’s essentially an infinitely changing calibration that will adapt to fit whatever ethanol content you choose to throw at it (within a predetermined range). Needless to say, flex fuel is the most common application for ethanol on the FA20DIT and that’s mostly down to the versatility and reliability of the setup.
Tuning: Due to the energy deficit per unit of ethanol vs gasoline, the stoichiometric ratio maintains an inverse relationship with ethanol saturation. As a result, more fuel volume is required to achieve the same combustion. For most cases, this is achieved via injector scaling. For the same reason, cranking and enrichment tables must be augmented to suit. With ethanol, the extra knock protection allows a tuner to optimize every part of the combustion process. Fueling can be leaned out. Ignition can be advanced. Boost can be increased. All of this, and more, comes together to increase both power potential and reliability.
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Thank you for reading my Op-Ed on the 2015+ Subaru WRX! I do hope you enjoyed the series as much as I enjoyed publishing it. Please reach out to me if you have any questions or would like more insight on any of the discussed topics.
Cheers!
-Clint
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