We installed the prototype of Tomioka Racing Catless Downpipe on the 2015 Subaru WRX. With the catless downpipe we expect to see gains in low end torque and engine response. We had previously installed the TR Engine Oil Cooler, Cobb Accessport V3, and re-flashed the ecu using the stage1 off-the shelf tune. These minor modifications showed improvements of 10whp and 25wtq from the stock 191whp and 225wtq. Also keep in mind that this was done on our DynaPack dyno which reads lower than most.
With the addition of the TR catless downpipe things got pretty interesting. We had gained 19wtq, but had lost 7whp. Although we had lost nearly the 10whp we gained from the stage 1 re-flah, the increase in low end torque and engine responsiveness was amazing. You can also see that the power is higher at the lower RPM to about 4500 RPM. One thing to note here is that this was not a pro tune. The car is still using the stage 1 map from Cobb. I would expect to see gains in both WHP and WTQ and smoothness with a pro-tune.
Video: 2015 WRX TR DP
As you can see, peak torque was reach much sooner, and the power was smoother up to 5000RPM where a custom tune will help.