Although modded Subaru’s have been a large part of the sport compact and motorsport scene for well over 20 years, there are some of you who are new to the world of Subarus, and many are the latest generation of young enthusiasts who got into an affordable turbocharged platform. Used WRX and even STI models are still very attainable, and many of these examples are believe it or not, are either stock, or still have proper mods left on the table. Now with the WRX and STI, there are common terms of that can be humorously synonymous with the EJ engine such as rod knock or blown head gaskets. One of the other common terms is heat soak. Before we get into what heat soak is, let’s unwind some of the schematics of how a turbocharger works:

 

 

The front of your turbocharger has the compressor wheel. The compressor wheel sucks in the air and compresses/forces air to the intercooler. The intercooler cools the air just before the air enters the intake manifold. On the back of the turbocharger, you have the exhaust wheel. The exhaust gases exit the head, through the exhaust manifold and through the exhaust housing where the exhaust wheel forces exhaust gases out of the downpipe. Now most turbocharged vehicles whether they be diesel trucks, a WRX, or any modern turbo Porsche will have intercoolers.

The issue with the intercooler design on Subaru’s especially modded WRX or STI models is their top-mount design. Now there is a method behind this design. The turbocharger sits on the upper passenger side corner of the engine bay where it directly connects to the intercooler. This helps reduce turbo lag as there isn’t pipes found in conventional front mount intercooler setups. The turbocharger can compress air directly to the intercooler where it also directly mounts to the throttle body. It’s an efficient design, yet the factory top mount intercooler is prone to heat soak.

 

WHAT’S HEAT SOAK?

 

Heat soak in terms of how it effects engine performance to your Subaru, is where the intercooler gets so hot that it fails to cool the intake charge temps going into the intake manifold. Therefor, you are only getting warm air entering your intake plenum. The cooler your intake charge temps are, the more power you will make through the motor, and you will also maximize the spool efficiency of your turbocharger. This is why we make more power in the fall/winter season because “boost weather” refers to cooler outside temps that will naturally provide the intercooler with faster cooling efficiency.

Because the turbocharger sits underneath the top mount intercooler on all turbocharged Subaru models, the intercooler is prone to more heat exposure because it is very close to the hottest component in the engine bay. Now this is more of an issue during the summer months. When your intercooler is heat soaked, you are limiting the performance of your mods. If you have an intake, turbo-back exhaust, a tune, and some fuel upgrades, you are making more power and boost. Naturally, the turbo reacts faster. You have to also consider that the OEM top mount intercooler is small by design, and that upgrades only accelerate the chances of heat soak.

 

GO BIG OR GO HOME

That’s right, the only remedy to combat heat soaking issues is to get a larger intercooler. Remember, with the EJ engine design with stock pistons and rods you are limited to just under 400 HP before you start blowing things up, and 330-350 HP is about the fun sweet spot on daily driven cars that use pump gas. Point being, we have several larger top mount setups that will be enough to suit your needs. Before we present some examples, let’s discuss the difference between front mount and top mount intercooler setups.

 

DIFFERENCE BETWEEN FRONT MOUNT VS TOP MOUNT INTERCOOLER SETUPS?

Front mount intercooler designs are found on just about all modified turbocharged vehicles with a front-engine layout. This will be the most effective option at cooling because you have all that incoming air coming towards the bumper, contacting the front surface of the intercooler.  With Subarus, you must rely on the air that enters the narrow slot on your factory hood scoop. The only drawback about front mount intercooler setups is that it blocks the airflow to your radiator. So, depending on how thick the front mount intercooler core is, it can cause a heating issue especially if you live in Phoenix in the middle of June. And the other minor issue is that there could be a hair of extra lag because the compressed air has to travel through the compressor side intercooler pipes, through the intercooler core, and through the pipes leading to the throttle body. But it’s really not noticeable. Front mount intercoolers are appropriate for those of you who are making 600+ horsepower through a rotated turbo setup, or if you road race, Time Attack, or HPDE your Subaru at weekend track events where temperatures will greatly increase.

Top mount intercooler setups in the aftermarket space, are going to be thicker to provide a cooler intake charge temp just before entering the throttle body, and can provide an adequate cooling temperature for those of you keeping power levels below 400 HP.

So, in a nutshell, a front mount intercooler setup is ideal for the following conditions:

• If you have basic bolt-ons but you track your Subaru where the engine will live in the upper RPM range for long periods of time.
• If you are making 500+ HP with an upgraded turbocharger that compresses a higher volume of air that surpasses the limits of a top mount intercooler core.
• If you simply want that aggressive race-inspired look.

 

A top mount intercooler is perfect for those of you who want something that is direct bolt-on, and will provide proper intake charge temperatures below 400 HP.

 

 

 

 

CLICK HERE TO SHOP FOR INTERCOOLERS

 

Whether if you want a proper top-mount setup, or if you want to go with a front mount intercooler design, we carry all the options to suit your needs. Let’s highlight some of the examples, as you cannot go wrong with either brand, or choice.

 

COBB Tuning Front Mount Intercooler Core 2015-2021 WRX/STI

 

 

GrimmSpeed Top Mount Intercooler 2002-2007 WRX / 2004-2021 STI

 

 

ETS Top Mount Intercooler 2022-2025 WRX

 

 

COBB Tuning Top Mount Intercooler 2015-2021 WRX

 

 

 

At the end of the day, you can’t go wrong with either choice whether it be a front mount or a top mount setup. The most important thing is that you are replacing that small OEM intercooler setup which will be a performance roadblock once you start upgrading. All of the examples that we carry are brought to you by the most established brands in the Subaru performance industry, guaranteed to improve the overall performance while maximizing the full potential of the rest of your upgrades.