Note: Designed for use with the 2002 STi High-Flow Bonnet Scoop

The goal for the Process West Top Mount Intercooler (TMIC) was simple: to engineer the best-performing aftermarket top-mount on the market. By analyzing common industry failures—such as poor ducting and inefficient core thickness—we have developed a cooling solution that sets a new standard for the Subaru platform.

The Critical Factor: Proper Ducting

A common mistake in the aftermarket is supplying a larger intercooler without the necessary ducting to support it. Installing a massive core while retaining the factory under-bonnet shroud is a waste of resources; the factory shroud simply cannot distribute air across the increased surface area.

For demonstration, we placed a factory shroud over our upgraded core:

As shown, approximately 50% of the upgraded intercooler receives no ambient airflow with the stock ducting. The image below shows the Process West solution: a custom-sized splitter that ensures 100% of the core receives direct, high-velocity ambient air.

The white outline in the image above illustrates the actual dimensions of the intercooler hidden beneath a factory WRX splitter. Without the correct ducting, the extra core size is essentially useless.

Optimised Core Thickness: 90mm vs. 114mm

Many competitors market 114mm (4.5") cores based on the "bigger is better" philosophy. However, for a top-mount application where air must make a sharp 90-degree turn through a bonnet scoop, excessive thickness creates too much resistance.

• Our Design: We utilize a 90mm (3.5") core.

• The Result: This thickness allows the air to actually "breathe" through the core rather than hitting a wall of resistance. This results in lower outlet temperatures and more consistent power.

High-Flow Silicone Y-Pipe

Standard aftermarket Y-pipes often suffer from uneven air distribution, favoring one side of the intercooler. Our custom-molded silicone Y-pipe is designed for perfect charge-air distribution across the entire entry tank.

Shown above: The complete system featuring the optimized Y-pipe, intercooler core, and custom splitter.

Data-Driven Performance

Dyno Testing

While dynos are notoriously difficult for top-mount testing due to limited scoop airflow, back-to-back testing against the factory unit on an '05 WRX revealed significant gains:

• Power Increase: The Process West system delivered 115.5kW, compared to the factory 107.5kW.

• Thermal Control: Even in static dyno conditions, the PW unit peaked at 51 °C, while the stock unit climbed to 66 °C.

(Power Graph: Before vs. After) ^^

(Temperature Graph: Before vs. After)

When subjected to three back-to-back runs to simulate heavy load, the factory intercooler outlet temps skyrocketed to 84 °C, whereas the Process West unit remained significantly more stable.

(Heat Soak Comparison Graph)

Real-World Street Testing

The true test happens on the road. During spirited mountain driving:

• Stock Intercooler: Temperatures peaked at 72 °C and continued to rise, resulting in a noticeable loss of engine "liveliness."

• Process West System: Despite aggressive driving, outlet temperatures never exceeded 43 °C.

Upgrade to the Process West TMIC Kit to ensure your Forester XT stays cool, responsive, and reliable under any conditions.