It’s been nearly two years since our first 2015 WRX development vehicle rolled into the shop. We’ve had a lot of fun with the car, and our team has developed a multitude of awesome components to aid in cooling, elevate power, and improve styling. Our product line is essentially complete, meaning we are done wrenching on our WRX. This is bitter sweet, as we will be picking up another vehicle to start the process once again. Before shipping out the WRX, we had one more project up our sleeves to extract a touch more power.
With our existing modifications, including our downpipe, intake, and cat-back exhaust system, most customers are making in the neighborhood of 290 whp and 310 wtq. Not bad for some simple bolt-on modifications and ECU tuning. We’ve been eyeing TGV modifications and have seen the impressive effects on Subarus from previous model years. We decided to open up the intake system on our 2015 to see if we could design a delete system that would deliver a few extra ponies.
Stock TGV System
If you are familiar with the function of the stock TGV (tumbler generator valve) system, feel free to skip the next couple paragraphs.
First, check out the image below showing the 2015 TGV assembly.
The TGV system sits between the plastic intake manifold and the cylinder head. Previous port-injection engines also had the injectors and fuel rail built into this piece. However, because the Subaru FA20 engine features direct injection, only the TGV butterflies and solenoids exist.
The TGV system can be considered a modern choke-like device. Its primary goal is to reduce emissions during cold-start conditions. The butterflies will close during a cold-start, which “tumbles” the airflow moving into the combustion chamber. This functions to speed up and stabilize the combustion process, effectively resulting in a cleaner burn. Improved emissions is always a positive outcome, but if you look closely at the image above, it is easy to see the obvious restriction this creates. Even with the valves open, the bar running across the center of the port produces a significant restriction to airflow.
Eliminating the internal portions of the TGV system opens up this chamber for greater airflow, which typically frees up some additional power.
Removing the Stock System
Our first task is to remove the stock system so we can evaluate the design. Our prototypes will be similar in style and shape, but they will be void of any TGV components (thus, a delete system). We need to capture dimensions from the stock components to help us create a model of our design. Because we are familiar with the FA20, we had the manifold off quickly. Check it out in the image below.
Here’s the underside of the manifold.
Check out a close-up of the flange surface for the TGV system.
If you look closely, you can see the rubber seal that creates a leak-free connection between the flat surfaces of the TGV assembly. A couple additional shots below show the TGV units once we removed them from the WRX.
Once these are removed, we are left with the engine bay shown below.
As with the intake manifold, this lower connection point also features rubber seals designed to mate with a flat surface. To ensure that all engine components fit perfectly, our TGV delete setup will be the exact height of the stock piece.
Delete Assembly – 3D Models
Using the dimensions captured from the stock TGV system and the intake manifold, we designed our first prototype in Solidworks. Check out a couple rendering shots of our initial prototype!
No valve shafts or butterflies in this piece! Our WRX will soon see smooth, unrestricted intake manifold flow!
Next time we will be 3D printing and test fitting our prototypes to ensure that our dimensional data provides perfect fitment.
Thanks for reading!