When upgrading your Subaru WRX’s forced induction system, the intercooler is one of the most critical components for consistent power delivery and engine protection. The two top mounts that dominate discussions in the Subaru community are the Forge 22-inch and the AMS 24-inch intercoolers. While both are designed to fit the GD, GE, and VA chassis WRX models, their distinct sizes, core architectures, and brand philosophies lead to very different real-world results. This article provides a deep, technical comparison of these two intercoolers, examining their impact on intake air temperatures (IATs), pressure drop, spool characteristics, and overall performance across various build levels.

Understanding Top Mount Intercoolers: Thermodynamics and Application

A top mount intercooler (TMIC) sits directly above the engine, relying on airflow from the hood scoop and the engine’s radiator fan to remove heat from the charge air. The primary goal is to lower the temperature of the compressed air from the turbocharger before it enters the intake manifold. Cooler air is denser, meaning more oxygen molecules enter each cylinder, enabling higher power outputs without detonation.

Two key metrics define intercooler performance: thermal efficiency (how much heat is removed) and pressure drop (how much restriction the intercooler adds to the intake flow). A larger core generally increases thermal capacity but can also introduce more pressure drop if the internal flow path is not optimized. The core design itself – bar-and-plate versus tube-and-fin – also influences durability, heat rejection, and weight. Understanding these trade-offs is essential when choosing between the Forge 22-inch and AMS 24-inch units.

Forge 22-Inch Intercooler: Robust Construction for Daily Reliability

The Forge 22-inch intercooler is built on a bar-and-plate core design, a construction method that uses flattened tubes separated by corrugated fins, all brazed together. This creates a very strong, heat-soak-resistant unit that excels in stop-and-go traffic and moderate boosts up to around 25psi. The core measures 22 inches in width, 10 inches in height, and 3 inches in depth – a conservative size that prioritizes fitment and airflow across the entire face of the hood scoop.

  • Core dimensions: 22” W × 10” H × 3” D (nominal)
  • Core type: Bar-and-plate, 100% welded construction
  • End tanks: Cast aluminum with smooth transitions to minimize turbulence
  • Outlet orientation: Driverside (compatible with stock intake and most aftermarket intakes)
  • Weight: Approximately 12 lbs (core + tanks)

Performance Characteristics of the Forge TMIC

In controlled testing on a stage‑2 WRX (turbo-back exhaust, Cobb Accessport tune, 20psi), the Forge intercooler typically reduces peak IATs by 30–40°F over the factory unit during a 3rd gear pull. More importantly, the bar-and-plate design resists heat soak during repeated pulls; whereas a tube-and-fin core might climb rapidly after a second run, the Forge core sheds heat quickly once airflow resumes. Owners also report a slight reduction in spool time (100–200 rpm earlier) due to the larger volume and smoother end tank transitions.

Where the Forge truly shines is daily driveability. The relatively compact face allows the stock hood scoop to fully cover the core, ensuring all incoming air passes through the intercooler. This means even in summer heat, the Forge can maintain consistent IATs without overshooting the factory intake temperature thresholds. It is a bolt-in upgrade that requires no trimming of the shroud or cutting of the intercooler brackets – a significant advantage for owners who want a simple, reversible upgrade.

For those pursuing higher horsepower, the Forge unit supports up to approximately 400 wheel horsepower (whp) on pump gas, with minimal pressure drop (around 0.5–0.8 psi at 25psi boost). Beyond that level, the 3-inch core thickness becomes a limiting factor for heat rejection, and pressure drop begins to increase exponentially.

AMS 24-Inch Intercooler: Maximum Cooling for High Horsepower Builds

The AMS 24-inch intercooler takes a different approach: a larger core area (24 inches wide by 11 inches tall) and a tube-and-fin core design. Tube-and-fin cores use oval or round tubes that are mechanically bonded to thin serpentine fins. This construction is inherently lighter than bar-and-plate and allows for more surface area per unit volume, which can translate to superior thermal efficiency when moving at speed. However, tube-and-fin cores are more susceptible to heat soak in low‑airflow conditions because the fins are thinner and less thermally massive.

  • Core dimensions: 24” W × 11” H × 3.5” D (nominal)
  • Core type: Tube-and-fin, with louvered fins for enhanced heat rejection
  • End tanks: Fabricated sheet aluminum, TIG welded
  • Outlet orientation: Driverside, but positioned slightly lower than stock – may require modification to the intake pipe or shroud
  • Weight: Approximately 10.5 lbs (core + tanks)

Performance Characteristics of the AMS TMIC

On the street, the AMS intercooler provides noticeably lower IATs at highway speeds compared to the Forge. In a 60–130 mph pull, the AMS often posts temperatures that are 10–15°F cooler than the Forge under identical conditions, thanks to its larger frontal area and more efficient fin geometry. This advantage becomes critical when pushing beyond 400 whp – for example, on a rotated turbo setup targeting 500–550 whp, the AMS top mount has proven capable of sustaining power without experiencing knock due to excessively high intake air temperatures.

However, there are trade-offs. The tube-and-fin core can heat soak more quickly during back‑to‑back dyno pulls or in bumper-to-bumper traffic. Some owners mitigate this through water spray systems or by upgrading the hood scoop and splitter to force more air through the larger core. Additionally, the AMS unit requires slight trimming of the intercooler shroud (plastic surround) and sometimes the hood latch support bracket for proper fitment. While not a major undertaking, it does mean the install is more involved than the Forge’s direct-fit design.

Pressure drop with the AMS intercooler is typically around 0.3–0.5 psi lower than the Forge at equivalent boost levels, due to the slightly thicker core and smoother air path through the tube-and-fin arrangement. For high flow turbo setups, every tenth of a psi counts, so this can translate to a modest gain in turbine efficiency.

Head-to-Head Comparison: Thermal Efficiency, Pressure Drop, and Real-World Testing

To provide a clearer picture, we compiled data from multiple independent forums (including NASIOC and Scoobypedia) and a few private dyno sessions. The following table summarizes the key differences under typical stage‑3 conditions (20psi boost, 75°F ambient):

Metric Forge 22” AMS 24”
Peak IAT reduction (vs stock, 3rd gear pull) 30–40°F 40–50°F
Pressure drop at 20psi 0.6–0.8 psi 0.3–0.5 psi
Heat soak resistance (low speed, repeated pulls) Excellent Moderate
Maximum recommended whp (pump gas) ~400 whp ~550 whp
Install complexity Bolt-in (no modifications) Minor trimming required
Weight (approx.) 12 lbs 10.5 lbs

These numbers confirm that the AMS 24-inch intercooler provides better raw cooling capacity for power‑oriented builds, while the Forge 22-inch offers more consistent daily performance and easier installation. The choice ultimately hinges on your power goals and driving habits.

Installation and Fitment Details

Forge 22-Inch: True Plug-and-Play

Removing the factory TMIC, installing the Forge unit, and reconnecting the charge pipes can be completed in under an hour on most WRX models. The cast aluminum end tanks are shaped to match the factory brackets and outlet flange location. No cutting, drilling, or adapter couplers are necessary. The hood scoop shroud fits perfectly over the core, maintaining the OEM sealing line. For owners who prefer a completely reversible upgrade, the Forge is the clear winner.

AMS 24-Inch: A Few Extra Steps

The larger core of the AMS protrudes slightly beyond the factory shroud window. To achieve proper airflow, you may need to trim the plastic shroud by about 1/2 inch on the passenger side and possibly trim the edge of the hood latch reinforcement bracket. Some owners also relocate the hood latch itself by a few millimeters, though many find that a slight bend of the support metal suffices. AMS provides a detailed instruction manual, and online communities have documented the process extensively. Expect the installation to take 1.5–2 hours for a first-timer with basic tools.

Additionally, the lower position of the outlet flange may require a different silicone hose or a slight modification to the intake setup if you are using an aftermarket cold‑air intake. It is advisable to test fitment of the intercooler before securing all brackets, to ensure the fan shroud and charge pipes do not rub.

Pricing, Warranty, and Brand Reputation

Both Forge Motorsport (UK) and AMS Performance (USA) are well‑respected in the automotive tuning industry. Forge has built a reputation for durable, OE‑quality replacements, while AMS focuses on producing race‑proven components used in competition vehicles, including time‑attack and drag cars.

  • Forge 22-inch intercooler: MSRP typically ranges from $749–$899, depending on fitment generation. Forge offers a 2‑year warranty on manufacturing defects.
  • AMS 24-inch intercooler: Priced slightly higher, around $899–$1,049. AMS provides a 1‑year warranty, but their customer support is often praised for helpfulness on technical questions.

While the initial cost difference is relatively small, the total cost of ownership may vary: the Forge’s easy installation can save you an hour of labor if you’re paying a shop, and its heat‑soak resistance means less need for auxiliary cooling (water spray, upgraded hood scoop). Conversely, the AMS’s lighter weight and higher thermal ceiling may justify the premium for high‑horsepower builders.

Making the Choice: Build Scenario Recommendations

Scenario 1: Stage 2 Daily Driver (Target: 300–350 whp)

For a WRX with a downpipe, intake, tune, and maybe a CBE, the Forge 22-inch intercooler is the ideal upgrade. It provides ample cooling for repeated pulls, resists heat soak during summer commutes, and installs in under an hour. The lower cost also leaves room for other supporting mods like a boost controller or upgraded fuel pump. Most owners in this power range report that the Forge completely eliminates the factory intercooler’s tendency to heat‑soak after just one or two pulls, which translates to consistent acceleration performance.

Scenario 2: Track Car / High Boost Build (Target: 400–550 whp)

If you are running a larger turbo (e.g., Blouch 1.5XTR or Dom 1.5), upgraded injectors, and an ethanol blend, the AMS 24-inch intercooler becomes the smarter choice. Its lower pressure drop and higher thermal capacity prevent the intake air temperature from spiking into knock territory during sustained wide‑open‑throttle runs. The small installation effort is a worthwhile trade‑off for the ability to maintain power through the entire powerband. Many track‑focused owners combine the AMS with a vented hood and a water spray system for even greater consistency.

Scenario 3: Mid‑Range Bolt‑On (350–420 whp)

This is the gray area where either intercooler could work. The deciding factor becomes driving style. If you prioritize quick spool and want a simple install without trimwork, the Forge will serve you well. If you anticipate future upgrades (e.g., going from a VF series to a rotated mount), the AMS offers headroom and might be more cost‑effective in the long run. Checking forums for your specific turbo setup can help – a Garrett GTX3071R, for example, tends to pair better with the larger AMS core.

Maintenance and Longevity Considerations

Both intercoolers require periodic inspection of the fin packs for debris (leaves, bugs, oil residue). The bar‑and‑plate core of the Forge is easier to clean with a gentle water stream, while the tube‑and‑fin core of the AMS should be cleaned with a low‑pressure air hose or a fine brush to avoid bending the thin fins. Additionally, check the silicone charge pipes and couplers annually for signs of cracking, especially if you are running high boost pressures.

Final Verdict

There is no absolute “best” intercooler – each serves a specific audience. The Forge 22-inch intercooler excels as a reliability‑focused upgrade for the vast majority of WRX owners who drive their cars daily and enjoy occasional spirited driving. Its bar‑and‑plate core, easy fitment, and heat‑soak resistance make it a top recommendation for builds up to 400 whp. The AMS 24-inch intercooler, with its larger core and tube‑and‑fin design, is the performance‑oriented choice for those chasing 450+ whp and demanding peak thermal efficiency on track days. Both units represent excellent engineering from their respective brands, and whichever you choose will be a substantial upgrade over the factory intercooler.

For further reading on intercooler theory and specific dyno results, check out the AMS Performance intercooler page and the Forge Motorsport Subaru intercooler lineup. Community discussions on NASIOC also provide hundreds of real‑world experiences to help guide your decision.