The Mitsubishi Lancer Evolution, or Evo, is a beloved performance car known for its turbocharged engine and all-wheel-drive system. One of the key components that can significantly enhance the performance of an Evo is the intercooler. Upgrading from the stock intercooler to a high-performance model like the CoolIT 24x12x3 can lead to substantial gains in horsepower and efficiency. This guide dives deep into the science, installation, tuning, and real-world results of this popular upgrade, helping you understand exactly what to expect and how to get the most out of your Evo.

Understanding Intercoolers: The Science of Cool Air

An intercooler is a heat exchanger used to cool the air compressed by the turbocharger before it enters the engine. Cooler air is denser, allowing for more oxygen molecules to enter the combustion chamber, which leads to better combustion and increased horsepower. But the benefits don't stop there. Lower intake air temperatures also reduce the risk of detonation (knock), allowing tuners to run more aggressive ignition timing and higher boost levels safely.

There are two main types of intercoolers: air-to-air and air-to-water. The Evo uses an air-to-air configuration, where ambient air flowing through the front-mounted intercooler core absorbs heat from the compressed charge air. Efficiency is measured by two key metrics:

  • Thermal Efficiency: How well the intercooler reduces the temperature of the compressed air compared to the ambient air. A high-efficiency core can drop charge temps by 70-80%.
  • Pressure Drop: The resistance the intercooler creates to airflow. A well-designed core minimizes pressure loss (typically under 1-2 psi) so the turbo doesn't have to work harder to overcome restrictions.

OEM intercoolers are often designed to balance cost, packaging, and moderate performance. They work well for stock boost levels and daily driving but quickly become a bottleneck when you increase power. Heat soak – where the core becomes saturated with heat during repeated hard pulls – is a common issue with stock units, leading to power loss and inconsistent performance.

Stock vs. Upgraded Intercoolers: Where the Evo Falls Short

The stock intercooler on the Evo (especially on Evo VIII, IX, and X models) is a bar-and-plate design, but it's relatively small. While it does an adequate job at factory boost levels (around 20 psi), it struggles at higher outputs. Common limitations include:

  • Small Core Volume: The stock core's dimensions limit its heat-soak capacity. After a few hard pulls, intake temperatures rise sharply, and the ECU pulls timing to protect the engine.
  • Thin Core: A thin core with fewer rows of tubes means less surface area for heat transfer, especially at high flow rates.
  • Restrictive End Tanks: Plastic or cast aluminum end tanks can create turbulence and uneven airflow distribution across the core.
  • Pressure Drop: At higher boost levels, the stock intercooler can cause a pressure drop of 2-3 psi, which saps power that could otherwise be used to make more boost.

Upgrading to a larger, more efficient intercooler like the CoolIT 24x12x3 addresses all these issues. With a larger frontal area (24x12 inches) and a thick 3-inch core, the CoolIT provides significantly more volume and surface area for cooling. The bar-and-plate construction with louvered fins increases turbulent airflow, improving heat transfer. Many aftermarket intercoolers also feature cast aluminum end tanks with smooth internal transitions to minimize pressure drop and distribute air evenly.

Benefits of the CoolIT 24x12x3 Intercooler

The CoolIT 24x12x3 intercooler is specifically designed for high-performance applications, making it an excellent choice for Evo enthusiasts seeking reliable power gains. Here are the key benefits in detail:

  • Size and Core Volume: With dimensions of 24x12x3 inches, this intercooler provides a massive increase in surface area and internal volume compared to stock. More volume means more time for heat transfer, and a larger frontal area allows more ambient air to flow through the core.
  • Core Design – Bar-and-Plate: The bar-and-plate design is favored in high-horsepower applications because it offers superior durability and heat rejection compared to tube-and-fin designs. The internal bars create a turbulent path for the charge air, breaking up the thermal boundary layer and maximizing heat transfer to the cooling fins. This design is less prone to deformation under high boost pressures.
  • Durability and Construction: The CoolIT intercooler is constructed from high-quality 6061 aluminum with TIG-welded end tanks. It can withstand the rigors of high-boost, high-heat environments, and the robust mounting brackets ensure a secure fit. The finish is typically a durable powder coat or bare aluminum for easy modification.
  • Measured Power Gains: Users report gains of 70+ wheel horsepower when the intercooler is paired with a proper tune and supporting modifications (like a fuel pump, injectors, and boost controller). Independent dyno tests show a reduction in intake air temperature by 30-50°F compared to stock during sustained pulls, which directly translates to more timing advance and higher boost levels without detonation.
  • Consistent Performance: Because of its large thermal mass and efficiency, the CoolIT intercooler resists heat soak. Even after multiple back-to-back pulls, intake temperatures remain much lower than with the stock unit, meaning you get consistent power on the street or track.
  • Pressure Drop Reduction: The smooth-flowing design and large core reduce backpressure on the turbocharger, lowering exhaust gas temperatures (EGTs) and improving spool characteristics. Many users note a quicker spool-up time after upgrading.

Installation Process: A Step-by-Step Guide

Installing the CoolIT intercooler is a weekend-friendly job for anyone with basic mechanical skills. The process is straightforward, but attention to detail is critical to ensure a leak-free, secure fit. Here’s a detailed guide:

Tools and Parts Needed

  • Socket set (metric, including extensions and swivel joints)
  • Screwdrivers (flathead and Phillips)
  • Pliers (including hose clamp pliers)
  • Torque wrench (for final tightening of clamps)
  • New silicone couplers and T-bolt clamps (often included with the CoolIT kit, but verify)
  • New intercooler piping (if not using stock piping with adapters – the CoolIT may require specific pipework)
  • Trim tool or utility knife (for slight modifications to the lower bumper support)
  • Jack and jack stands (for better access)
  • Anti-seize compound (for threaded connections)

Preparation and Safety

  1. Disconnect the negative battery terminal.
  2. Remove the front bumper cover (or at least the lower grille and undertray) to access the intercooler. On many Evo models, this involves removing several plastic push clips and screws.
  3. Support the vehicle securely on jack stands.

Step 1: Remove the Stock Intercooler

  1. Loosen the clamps on all turbo outlet pipes and intake manifold inlet pipes connected to the intercooler.
  2. Disconnect any hoses, such as the blow-off valve recirculation hose or the charge air temperature sensor (if equipped).
  3. Unbolt the stock intercooler from its mounts. Usually two or three bolts hold it in place. Carefully slide the intercooler downward and out. You may need to rotate it slightly to clear the radiator support.
  4. Inspect the condition of your stock piping. If it’s old and cracked, consider replacing it with high-quality silicone hoses.

Step 2: Prepare the New Intercooler

  • Before installation, check the fit of the CoolIT intercooler by placing it in the vehicle behind the bumper support. Some minor trimming of the lower plastic support may be required. Use a trim tool or a sharp utility knife to shave off any interfering plastic.
  • Assess the mounting location. The CoolIT intercooler often uses its own bracket set or utilizes factory mounting points. Follow the included instructions for your specific Evo model.
  • Attach the supplied silicone couplers and T-bolt clamps loosely to the inlet and outlet of the intercooler for easier positioning later.

Step 3: Install the CoolIT Intercooler

  1. Position the intercooler in place and secure it with the mounting hardware. Tighten the bolts to spec – do not overtighten aluminum brackets.
  2. Connect the charge air piping. If the CoolIT intercooler uses larger inlet/outlet sizes (commonly 2.5 or 3 inches), you may need new piping. For a direct fit, ensure your pipes match the orientation of the intercooler outlets. Many kits include short piping to adapt from the stock turbo outlet to the new intercooler.
  3. Connect all couplers and tighten the T-bolt clamps evenly. Do not fully tighten until all pipes are aligned.
  4. Reconnect any sensor hoses. If the stock charge air temperature sensor is mounted in the intercooler piping, ensure you install it in the new pipework (often a bung is provided).
  5. Double-check that no pipes are contacting the radiator, fan, or body panels. Clearance issues can cause abrasion and eventual failure.

Step 4: Final Checks and Leak Testing

  1. Once everything is assembled, go back and tighten all T-bolt clamps to the recommended torque (usually around 40-50 in-lbs). Do not overtighten, as it can damage the couplers.
  2. Reinstall the bumper cover, undertray, and any other removed components.
  3. Reconnect the battery.
  4. Start the engine and let it idle. Listen for any air hissing sounds that indicate a leak. A boost leak tester is highly recommended – you can build one for under $20 using PVC caps and an air compressor. Pressurize the intake system to 10-15 psi and spray soapy water on all pipe connections. Bubbles indicate a leak.

Tuning for Maximum Performance: It's Mandatory

After upgrading the intercooler, it is not optional to have the vehicle tuned properly. The stock ECU calibration is designed around the limitations of the stock intercooler. With dramatically lower intake air temperatures and higher airflow potential, the engine will run lean if not retuned. More importantly, you'll want to take advantage of the cooling capacity by increasing boost and ignition timing.

What a Professional Tune Does

  • Fuel Maps: The tuner will adjust the air-fuel ratio to maintain safe, powerful combustion. With more airflow, fuel delivery must be increased (via larger injectors and a higher-flow fuel pump) to keep the mixture from leaning out.
  • Boost Control: Many tuners raise boost levels to 25-30 psi (depending on fuel and turbo setup) to use the extra cooling capacity effectively.
  • Ignition Timing: Cooler air allows more aggressive timing without knock. Tuners can advance timing to extract more power.
  • Load and RPM scaling: The ECU's volumetric efficiency tables need to be recalibrated for the new intercooler's characteristics.

Supported Modifications

To safely achieve the 70+ wheel horsepower gains, you'll typically need:

  • Aftermarket fuel pump (e.g., Walbro 255 or AEM 340)
  • Larger fuel injectors (800-1000 cc/min for pump gas, larger for E85)
  • Boost controller (electronic preferred for precise control)
  • Custom tune via ECUFlash, Cobb Accessport, or a standalone ECU (e.g., AEM, Motec)

Many Evo owners combine the CoolIT intercooler with an upgraded turbocharger, exhaust system, and intake. The intercooler is rarely the only power adder, but it is a foundational upgrade that supports all others.

Real-World Performance Gains: What Owners Report

Evo forums and communities are filled with success stories from the CoolIT 24x12x3 intercooler upgrade. Here's a summary of common feedback:

  • Quicker Throttle Response: Many note that the car feels more responsive off-boost and during transient throttle changes. This is due to reduced pressure drop and lower intake temps.
  • Improved Power Delivery: Power feels smoother and holds longer to redline. The intercooler helps maintain boost pressure at high RPM by reducing restriction.
  • Enhanced Reliability: During high-performance driving (road courses, autocross, drag racing), the CoolIT intercooler keeps IATs in check. Owners report losing less power after consecutive pulls compared to stock.
  • Dyno Results: Independent dyno sheets show gains of 40-70 whp when upgrading from a stock intercooler on a tuned Evo with basic bolt-ons. When combined with a larger turbo, the intercooler supports even bigger numbers.

For example, a well-known Evo tuning shop posted a comparison with a completely stock car: after a tune and the CoolIT intercooler, the car gained 65 whp and 80 lb-ft of torque on 93 octane. The IAT dropped by 40°F during the pull.

Common Pitfalls and How to Avoid Them

  • Ignoring Leaks: A boost leak after intercooler installation can cause poor performance and even engine damage. Always pressure test the system.
  • Skipping the Tune: Running a stock tune with a more efficient intercooler can cause the engine to run lean due to increased air density. This can lead to detonation. Always retune.
  • Overlooking Hoses: Old, worn silicone hoses can collapse under boost or crack. Replace with high-quality units rated for high temperatures and pressure.
  • Fitment Issues: Some aftermarket intercoolers require trimming of the bumper support or crash bar. Not trimming enough can lead to poor airflow or rubbing. The CoolIT is known for good fitment, but verify with your specific model year.

Conclusion: Is the CoolIT 24x12x3 Intercooler Worth It?

Upgrading to the CoolIT 24x12x3 intercooler is a smart move for any Evo owner looking to enhance their vehicle's performance. The combination of a large core, efficient bar-and-plate design, and robust construction addresses the biggest weaknesses of the stock intercooler: heat soak, pressure drop, and limited airflow. With significant horsepower gains of 70+ wheel horsepower, improved reliability under sustained boost, and consistent power output, this intercooler upgrade provides excellent value for the money.

It is not the cheapest upgrade, but it is one of the most impactful. It prepares your Evo for further modifications and protects the engine from excessive heat. When paired with a proper tune and supporting modifications, the CoolIT intercooler transforms the driving experience. Whether you are building a daily driver that sees occasional track time or a full track-dedicated machine, this intercooler should be high on your list. For more technical details and customer reviews, check the CoolIT Performance official site and enthusiast forums like EvolutionM.net.