Series: 2015+ Subaru WRX Modification (Pt.3)
Hello and welcome to my Op-Ed on the 2015+ Subaru WRX! This is part 3 of a 10 part series that plans to encompass all of the information you will need to make informed decisions regarding the best upgrade path for your vehicle.
This week, I will be giving an in-depth overview of Electronic Boost Control Solenoids, Turbochargers, Intercoolers, and Charge Pipes. 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.
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.
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.
Modifications and Preferred Brands
Electronic Boost Control Solenoid
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.
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.
Intercooler / Charge Pipe
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.
Tune in next week (02-22-2021 @ 12:00 EST) where I will be giving an in-depth overview of Intake Manifolds and Tumble Generator Valves. 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.