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2004 Subaru WRX - Keeping Under Pressure Cool - Tech Knowledge

What To Expect From Upgrading Your WRX's Intercooler

The golden rule of tuning? If you want to increase the performance of your car, you've got to cover all the bases. Want to add forced induction? Better add fuel as well. Want to make it accelerate faster? Without crashing? Then upgrading the brakes is a must. And so it goes with raising the boost of a factory turbocharged car; don't think it's as easy as pushing a button on that aftermarket boost controller of yours-you've got to deal with the consequences. The first of which, is likely going to be heat.

Compressing any gas, like atmospheric air, increases its temperature-especially when the mechanism for compression is a hot, exhaust gas-driven turbocharger. Radiating as much heat away from a turbocharged car's intake charge as possible is essential for keeping it alive and making power. OEMs understand this, and nearly all of them include some type of intercooler setup in their turbocharged cars, but the problem is that they're usually most efficient at stock boost levels; when you decide to increase boost to make more power, increasing the efficiency of your car's intercooling system proportionally is a must.

The '02 and newer WRX top-mount intercooler is a great example of one that handles stock power levels adequately, but responds poorly to increased demands. Its top-mount design doesn't intrude upon radiator or A/C exchanger efficiency, and combined with the OE hoodscoop, radiates enough heat to adequately cool intake charge at stock boost levels. Its most impressive contribution lies in how small its charge piping is-meaning very little pressure drop before the throttle body, and near-instant throttle response. But, as boost pressure is ramped up, the small surface area of the WRX's intercooler, and small amount of incoming ambient air limited by its hoodscoop, do a poor job of radiating increased temperatures past the stock level-limiting benefits found by increasing boost in the first place. There are larger, more efficient top-mount intercoolers and hoodscoops on the aftermarket, but they'll never offer as much surface area or direct airflow as a properly designed front-mount unit will. The transition to FMIC is an absolute prerequisite to building for big power, via an upgraded turbo and high-boost tuning, but is there any benefit to making the switch ahead of time? Can adding an FMIC bring any power gains to a lightly modded car? Can it increase tuning potential in stock turbo applications?

On the dyno, the benefits of the upgrade were apparent. All testing was conducted with the hood closed, to allow for best airflow to the stock top-mount unit, and for consistent parameters all around. Intake charge temperatures dropped significantly after the installation of the Perrin FMIC, and radiator efficiency wasn't negatively affected at all. Maximum boost was mechanically limited to just over 13 psi for the stock TMIC test, but after installing the Perrin FMIC, max boost fell about 1 psi; indicative of the slight pressure drop commonly found by upgrading to larger intercoolers. Dialing up pressure to put the FMIC on par with the TMIC showed sizeable low- and mid-range gains-resultant of Perrin's cooler charge-but top-end power couldn't match stock levels. Looking closely at timing and knock data between the two runs, Alfred points out that the power drop is a product of the previous tune no longer being optimized for the changes brought by the larger FMIC, and points out that it should become a non-issue with a good re-tune.

In summary, the conversion to FMIC proved its worth to our '04 WRX through the numbers-cooler temperatures all around, increased immediate power, and the ability to make even more with tuning, and support nearly any imaginable turbo upgrade. Plus, it looks mean. Not that that should ever be a deciding factor when considering adding performance parts to your ride...but it helps!

INTAKE TEMPERATURE (F) PERRIN STOCK
109 121
COOLANT TEMPERATURE (F) 210 216
AVERAGE BOOST 12.1 12.1
MAXIMUM HORSEPOWER 204.6 202.8
MAXIMUM TORQUE 206.7 194.8
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