The 1G Eclipse (1990–1994) remains a beloved platform in the DSM community, largely due to its turbocharged 4G63 engine. Among the most common upgrades for these cars is the aftermarket intercooler. But is it really worth the money? This article breaks down how intercoolers work, the critical differences between stock and aftermarket units, the impact of core size on cooling and power, and the real-world gains you can expect. We also cover fitment, supporting modifications, and cost considerations so you can make an informed decision for your build.

Understanding Intercoolers

An intercooler is an air-to-air heat exchanger placed between the turbocharger compressor outlet and the engine’s intake throttle body. Its job is to reduce the temperature of compressed intake air. When air is compressed, it heats up; hot air is less dense, containing fewer oxygen molecules per volume. By cooling the air, the intercooler increases air density, allowing more oxygen into the combustion chamber. More oxygen means you can add more fuel and produce more power without knocking.

Intercooler efficiency is measured by two main metrics: cooling efficiency (how much the air temperature drops relative to ambient) and pressure drop (how much the air pressure is reduced as it flows through the core). A good aftermarket intercooler balances high cooling efficiency with low pressure drop. On the 1G Eclipse, the factory intercooler was adequate for stock boost levels (around 9–12 psi), but it quickly becomes a bottleneck when boost is increased or a larger turbo is installed.

Stock vs Aftermarket Intercoolers

The 1G Eclipse came from the factory with a side-mount intercooler (SMIC) located on the passenger side of the engine bay. It is small, with a core roughly 12" x 6" x 2.5". It uses a tube-and-fin design with plastic end tanks. While it works for stock power, it has several limitations:

  • Heat soak: Being tucked behind the bumper and near the radiator, it quickly heat-soaks in stop-and-go traffic or during repeated hard pulls.
  • Small core: Limited surface area means it cannot cool high volumes of boosted air efficiently.
  • Restrictive piping: The factory routing has several sharp bends and uses small-diameter pipes (2.0”–2.25”), choking airflow.
  • Plastic end tanks: Prone to cracking under higher boost pressures.

Aftermarket intercoolers are almost always front-mount intercoolers (FMICs) mounted in front of the radiator. They use larger cores, often bar-and-plate construction, and aluminum end tanks. The typical upgrade path is a 24” x 6” x 3” to 28” x 9” x 3” core. Aftermarket intercoolers also allow for smoother, larger-diameter piping (2.5” or 3.0”), reducing restriction and improving airflow.

Core Sizes Explained

Core size is the most visible difference between intercooler options. But size alone doesn’t tell the whole story—core thickness, fin density, and internal flow path also matter. Here’s how the common sizes stack up for a 1G Eclipse:

Small Core (e.g. 24" x 6" x 3")

This size is roughly 1.5 times the volume of the stock side-mount. It fits behind the stock bumper with minimal trimming and works well for cars running a 16G turbo or smaller, at boost levels up to 20 psi. Power gains are modest, typically 5–10% over the stock intercooler at the same boost level, due to reduced heat soak and lower intake temperatures.

Medium Core (e.g. 28" x 7" x 3.5")

This is the sweet spot for many 1G owners. It offers about double the core volume of the stock intercooler. It fits with some bumper reinforcement trimming and works well with upgraded turbos like the 20G or small frame Garretts (GT35R). Expect 10–20% power gain over stock when running 20–25 psi. The larger surface area keeps intake temps low even on back-to-back pulls.

Large Core (e.g. 30" x 10" x 3.5")

These are for high-horsepower builds (400+ whp). They fill the entire front opening of the car and often require cutting the bumper support and relocating the oil cooler or A/C condenser. They flow enough to support 30+ psi and turbos like the GT42 or HX40. Power gains can be 20–30% or more compared to a stock intercooler, but only when combined with a large turbo, upgraded fuel system, and proper tuning. Oversizing can cause excessive pressure drop if the core is too thick or poorly designed.

Bar-and-Plate vs Tube-and-Fin

Nearly all performance aftermarket intercoolers use a bar-and-plate design. This construction is more durable, has better heat transfer capability, and holds up to high boost without deforming. Tube-and-fin intercoolers are lighter and can flow better with less pressure drop, but they are less efficient at cooling and more fragile. For a street-driven 1G that may see track time, bar-and-plate is the recommended choice.

Power Gains and Supporting Mods

Simply bolting on a larger intercooler without changing the turbo or boost level will yield limited gains—perhaps 5–15 horsepower from reduced heat soak. The real benefit comes when you increase boost. A stock side-mount becomes a significant restriction above 15 psi, forcing the turbo to work harder (higher turbine backpressure) and heating the intake air far beyond the compressor’s limits. An aftermarket FMIC allows you to run higher boost with cooler air, directly translating to more power.

For example, a 1G with a 16G turbo, 2.5” exhaust, 550cc injectors, and an aftermarket intercooler can safely run 20–22 psi on pump gas, making around 320–350 whp. The same setup with the stock side-mount would struggle to run 18 psi without knock, limiting power to about 280 whp. That’s a 40–70 whp gain from the intercooler alone (along with supporting mods).

Important: The intercooler alone will not unlock power if other parts of the system are stock. You need a way to control boost (MBC or electronic), adequate fuel delivery (pump + injectors), and tuning (ECU chip, SAFC, or a standalone like DSMLink). An intercooler helps prevent knock, allowing you to run more ignition timing and leaner air/fuel ratios, which is where the power comes from.

For a more extreme example, a 1G with a GT35R running 30 psi and an Alkycontrol methanol injection system can make 600 whp with a large FMIC. The intercooler is key to keeping intake temps under 130°F even on high-boost passes.

Considerations for Installation on a 1G Eclipse

Installing an aftermarket FMIC on a 1G requires some fabrication. Here are the main areas to address:

Fitment and Clearance

The 1G has a tight engine bay. A typical 28” wide core will fit between the frame rails but may require trimming the lower bumper support. Many aftermarket kits are designed specifically for the 1G and include brackets that mount to the radiator support or frame. You also need to choose a core thickness that clears the A/C condenser and radiator—3.0” is usually fine, 3.5” can be tight.

Piping Routing

Most aftermarket intercooler kits for the 1G route the intake from the turbo, across the front of the engine, into the passenger side of the intercooler, then out the driver side and up to the throttle body. This requires cutting the battery tray or relocating the battery (often to the trunk). Short-route pipings that go through the driver’s side wheel well are also popular and keep pipe lengths minimal for faster spool.

Piping diameter: Match the pipe size to your turbo outlet and throttle body opening. 2.5” pipes are standard for 400–500 whp. 3.0” pipes are needed for larger turbos but can cause a slight lag on smaller turbos. Use silicone couplers and T-bolt clamps for a leak-free setup.

Bumper Support and Appearance

Large FMICs require cutting the front bumper beam (the metal bar behind the bumper cover). Some owners replace the stock beam with a lighter tubular unit. The intercooler itself will be visible through the front bumper opening, which many consider a cosmetic improvement. You can also add a mesh grille to protect the fins from debris.

Oil Cooler and A/C

If your 1G has an oil cooler (most turbo models do), it may block part of the intercooler core. You can relocate the oil cooler to the side or buy a slimline oil cooler. A/C condenser fans may need to be removed or upgraded to pull-through fans if the intercooler blocks the condenser. For dedicated track cars, some remove A/C entirely.

Cost vs Benefit Analysis

Aftermarket intercooler kits for the 1G range from $200–$600 for a complete piping kit with core (such as a CX Racing or Mishimoto unit), up to $800–$1200 for high-end units from companies like ETS, PWR, or Spearco. The budget kits work well for 300–450 whp, while the high-end cores offer lower pressure drop and better heat rejection for 500+ whp.

Compare that to the cost of engine damage from detonation: a blown head gasket or melted piston easily costs $2000+ to repair. An intercooler is relatively cheap insurance. Even if you never push the car hard, the improved power delivery and consistency on hot days make it a worthwhile upgrade.

There is also the option of upgrading to a larger side-mount intercooler from a later model (2G DSM or Evo VIII/IX). These are bolt-in modifications but still limited in size compared to a proper FMIC. They are cheaper ($100–200) but offer less performance.

Conclusion

For a 1G Eclipse turbo owner, upgrading to an aftermarket front-mount intercooler is one of the best performance investments you can make. It reduces intake temperatures, allows higher boost without knock, and supports future power upgrades. The key is choosing the right core size for your power goals: a 24”x6”x3” for a mild street car (<300 whp), a 28”x7”x3.5” for a strong street/strip car (350–450 whp), and a 30”x10”x3.5” for a serious race build (500+ whp).

Do not neglect supporting modifications—boost control, fuel system upgrades, and tuning are necessary to realize the full potential. And always ensure proper fitment before cutting. When done correctly, an aftermarket intercooler transforms the 1G from a fun but heat-soaked cruiser into a consistent, powerful machine ready for highway pulls and track days alike.

For more detailed install guides and community dyno results, check out this DSMTuners comparison thread and the ECMTuning intercooler wiki for pressure drop data. Also, consider ETS’s DSM-specific kits for a proven option.