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Series: 2015+ Subaru WRX Modification (Pt.4 - Intake Manifold / TGV Housing)

February 22, 2021

2015+ Subaru WRX Modification (Pt.4 - Intake Manifold / TGV Housing)

Series: 2015+ Subaru WRX Modification (Pt.4)

     Hello and welcome to my Op-Ed on the 2015+ Subaru WRX! This is part 4 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 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.


     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

Intake Manifold

     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.

IAG Complete Upper and Lower TGV Housing Silver - 15-21 WRX


     Tune in next week (03-01-2021 @ 12:00 EST) where I will be giving an in-depth overview of Built Blocks and Downpipes. 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.