A Front-Mount for the 2015 STi, Part 4: Final Prototype Fitting

Posted: February 17, 2016

Categories: Subaru STi Front-Mount Intercooler 2015+

Tags: turbo, teammishi, subaru, sti, scca, race, mishimoto, intercooler, featured, fast, ej257

Putting together our final prototype was a bit easier for this project compared to other front-mount intercooler (FMIC) kits our team has developed. As mentioned in previous segments, we used the crash beam and intercooler from our 2015 WRX kit. Now we've worked up some functional prototype piping for a final test fit.

First, let's take a quick look at each portion of the kit.

Intercooler and Crash Beam

The intercooler core is the key component in any intercooler kit. This core has provided significant air temperature drops during our testing on the WRX, and we expect the same results with the STi.

Mishimoto STi intercooler and crash beam

This core was engineered to provide an ideal balance between heat transfer and airflow.

Silicone Components

Mishimoto 2015 STi front-mount intercooler silicone hoses

Kit Accessories

A few brackets and some hardware help piece this kit together for a solid, durable installation. We are also including a BPV (bypass valve) adapter flange so we can utilize the stock valve.

Mishimoto 2015 STi front-mount intercooler hardware and accessories

The small, round, CNC-machined component is the sound symposer delete plug. A simple plastic plug would work here, but we decided to flex our CNC muscles to create a more unique plug.

Mishimoto 2015 STi parts

Intake Pipe and Filter

Since our intercooler pipe route passes through the stock airbox, an aftermarket intake must be used. For those of you who don't already have an aftermarket intake for your STI, we developed an intake pipe and filter setup that are compatible with this FMIC application.

Mishimoto 2015 STi parts

Intercooler Piping

The intercooler piping was the developmental highlight for this project. Let's take a look at our finished product.

Mishimoto 2015 STi front-mount intercooler piping

From an aesthetic standpoint, the piping looks fantastic. The true test will be when we install these pipes and verify fitment.

Full Kit

Mishimoto STi intercooler kit

Kit Installation

Time to bolt our kit onto the STi and verify fitment.

Mishimoto 2015 STi front-mount intercooler kit installed

Mishimoto STi intercooler kit installed

All components within the engine bay fit perfectly. Our sound symposer delete piece fits nicely and looks fantastic.

Mishimoto 2015 STi parts

One of the challenges encountered with our pipe fabrication centered around the entry into the bumper area due to tight fitment. Thanks to diligence on the part of our engineering team, everything bolted into place perfectly.

Mishimoto 2015 STi parts

Mishimoto STi intercooler kit installed

We've built some slight adjustment allowance into this kit to provide for easy installation. Both the intercooler core and piping have flexibility, allowing the user to adjust for great fitment.

Testing Data

Cold weather conditions are not optimal for testing the efficiency of a heat exchanger. Unfortunately, the timing of this project places completion right in the middle of winter.

For now, we will be using our positive results from WRX testing to support this intercooler core. Testing data may vary slightly, however we do expect this kit to drop temperatures in a similar manner.

Below is a temperature plot from our 2015 WRX FMIC testing which compares stock top-mount intercooler (TMIC) outlet temperatures to that of our FMIC.

Outlet temperatures per RPM comparison

Temperatures in the test above rise around 15°F above ambient in our shop, and this is with a low-powered blower fan producing around 30-40 mph wind speeds. This equates to a drop of nearly 40°F compared to the stock intercooler.

Later in the summer we took our testing on the road and we were able to achieve intake temperatures within 3°F of ambient temperatures during the entirety of back-to-back third gear pulls.

We have 100% confidence we will see extremely similar results with the FA20 swapped for the EJ engine in the STi. Once temperatures start rising this year we can begin making plans for some road testing with this kit.