The Evolution of Forced Induction on the Mitsubishi 3000GT

The Mitsubishi 3000GT (and its Dodge Stealth sibling) remains a landmark in 1990s Japanese sports car engineering. Its twin-turbocharged 3.0L V6 — the 6G72 — delivered competitive power from the factory, but heat management was always its Achilles’ heel. The stock intercoolers, while adequate for stock boost levels, quickly become a bottleneck when owners seek more power. Upgrading to a Greddy intercooler is one of the most effective and popular modifications for addressing this limitation. This guide provides a comprehensive look at the performance benefits, installation process, and necessary tuning steps to make the most of this upgrade.

Why the Stock Intercooler Falls Short

Factory intercoolers on the 3000GT are small, side-mount units tucked behind the fog lights. Their limited core volume and restrictive end tanks lead to significant heat soak under sustained boost, causing intake air temperatures (IAT) to climb rapidly. As IAT rises, air density drops, robbing the engine of oxygen and increasing the risk of knock. On a stock tune, the ECU responds by pulling timing, reducing power. With a more aggressive tune, high IATs can lead to detonation and engine damage. A Greddy front-mount intercooler (FMIC) replaces these undersized units with a single, large core mounted in front of the radiator, directly in the airflow. This drastically reduces IATs and provides a consistent supply of dense, oxygen-rich air.

How a Front-Mount Intercooler Works

Compressed air from the turbochargers can exceed 300°F under heavy load. As this hot air passes through the intercooler, heat is transferred to the cooler ambient air flowing through the core. The Greddy intercooler uses a bar-and-plate core design, which is more efficient and durable than the tube-and-fin construction found in many stock units. This design allows for greater heat dissipation and lower pressure drop, meaning the engine doesn’t have to work as hard to push air through the system. The result is cooler, denser air entering the intake manifold, which directly translates to more power and a reduced chance of knock.

Greddy Intercooler Features and Benefits for the 3000GT

Greddy has long been a trusted name in Japanese performance tuning, and their intercooler kits for the 3000GT are engineered specifically for this chassis and engine family. Key features include:

  • Large bar-and-plate core with high-density fin count for maximum heat rejection.
  • Cast aluminum end tanks with smooth internal transitions to minimize turbulence and pressure loss.
  • Precision-polished piping designed to maintain factory-like routing, reducing the need for extensive modifications.
  • Reinforced mounting brackets to withstand the rigors of daily driving and track use.
  • Complete silicone hose and clamp kit for secure, leak-free connections.

Owners often report IAT reductions of 50–80°F compared to the stock side-mounts, even under hard pulls. The improved thermal efficiency allows for more aggressive boost levels when combined with proper tuning.

Bar-and-Plate vs. Tube-and-Fin

While many budget intercoolers use tube-and-fin cores that are lighter but less efficient at heat transfer, Greddy’s bar-and-plate construction excels in both airflow and thermal capacity. The bar-and-plate design also has thicker internal walls, making it more resistant to rock strikes and debris damage — an important consideration for a part mounted low in the front bumper.

Real-World Performance Gains

The performance improvement from a Greddy intercooler depends on the vehicle’s current modifications and tuning. On a nearly stock 3000GT with the boost set to 12–14 psi (stock is around 10 psi), owners can expect:

  • 15–30 whp gain from reduced heat soak alone, particularly during repeated runs.
  • Consistent power delivery without the drop-off experienced with stock intercoolers after the first few seconds of boost.
  • Lower engine temperatures, which can prolong the life of the turbos and engine internals.
  • Improved throttle response due to denser intake charge and reduced system volume.

For a more heavily modified car with upgraded turbos, fuel system, and an ECU tune, the intercooler becomes even more critical. Many 500+ whp 3000GT builds rely on Greddy’s larger cores to keep IATs in check.

Installation Guide: Step-by-Step

Installing a Greddy intercooler on a Mitsubishi 3000GT is a weekend project for a home mechanic with moderate experience. The kit is designed to be a direct fit, but some patience and attention to detail are required. Below is a thorough installation guide.

Tools and Parts You’ll Need

  • Socket set (metric, 10mm, 12mm, 14mm, 17mm)
  • Wrenches and ratcheting wrenches
  • Flathead and Phillips screwdrivers
  • Interior trim removal tools (for bumper clips)
  • Jack and jack stands
  • Dremel or cutoff wheel (for trimming plastic support, if needed)
  • New coolant (if you disconnect radiator hoses)
  • Anti-seize compound for bolts
  • Shop rags and safety glasses

Step 1: Safety First

Park the vehicle on a level surface, disconnect the negative battery terminal, and allow the engine to cool completely. The intercooler system is located low in the front, so raise the front of the car securely on jack stands. Never rely on a jack alone.

Step 2: Remove the Front Bumper and Stock Intercooler Assembly

Begin by removing the front bumper cover. On the 3000GT, this involves removing screws in the wheel wells, plastic rivets along the top lip, and a few bolts behind the lower grille. Carefully pry the bumper free and set it aside. With the bumper removed, you’ll see the factory intercooler pipes, turbos, and the two small side-mount intercoolers. Remove the factory intercoolers by unbolting the brackets and disconnecting the rubber hoses. Also remove the stock intercooler ducting and any plastic shrouding that obstructs the new intercooler’s placement. It’s helpful to label the OEM hoses and bolts for reassembly if you ever revert to stock.

Step 3: Prepare the Core Support Area

The Greddy intercooler is larger than the combined volume of the two stock intercoolers. Some owners find that the plastic under-tray or the metal front bumper support beam requires minor trimming. Use a Dremel or cutoff wheel to remove any plastic tabs that interfere with the intercooler’s position. Do not cut the metal crash beam unless absolutely necessary — Greddy kits are designed to fit within the stock structure. If you have an aftermarket bumper or a Stealth, clearance may differ.

Step 4: Mount the New Intercooler

Slide the Greddy core into place, ensuring the outlet and inlet ports are oriented correctly (typically driver’s side inlet from the turbos, passenger side outlet to the throttle body). Use the supplied brackets to secure the intercooler in the lower grille opening. Tighten the bolts gently — over-tightening can distort the brackets. Verify that the intercooler sits level and does not contact the radiator, condenser, or any moving parts. A small gap of at least 1 inch between the intercooler and the radiator is desirable to allow airflow.

Step 5: Connect the Piping System

Greddy kits come with pre-bent aluminum pipes. Start by connecting the pipe from the driver’s side turbo to the intercooler inlet. Then route the outlet pipe up to the passenger side throttle body. Each connection should use a silicone coupler and T-bolt clamp. Tighten clamps securely, but avoid pinching the silicone. Ensure that the pipes are positioned away from belts, pulleys, and the radiator fan. If a pipe rubs against a sharp edge, wrap that section with silicone tape or split loom. Double-check that all connections are leak-free after the first test drive.

Step 6: Reassemble the Front End and Test

Reinstall the front bumper cover, taking care to clip all fasteners properly. Some bumper trimming may be needed if the intercooler core protrudes. Reconnect the battery. Start the engine and let it idle while checking for boost leaks — listen for hissing and feel along connections for escaping air. If you have a boost leak tester, pressurize the system to 15 psi and use soapy water to spot bubbles. Fix any leaks before driving.

Tuning for Maximum Gains

Simply bolting on a larger intercooler without tuning is safe, but you will not capture its full potential. The stock ECU is programmed for the cooling characteristics of the small side-mounts and will not automatically compensate for the dramatically lower IATs. To truly benefit, consider the following:

  • ECU Remapping: A custom tune via a flashable ECU (like 3SX Performance provides options) can optimize ignition timing and fuel delivery for the denser intake charge. Expect gains of 15–30 hp on the same boost level after a proper tune.
  • Boost Controller: With the intercooler’s improved efficiency, you can safely increase boost. A manual or electronic boost controller set to 14–15 psi (with supporting fuel mods) yields excellent returns without stressing the stock turbos too much.
  • Wideband O2 Sensor: Monitoring air-fuel ratios is critical. Aim for 11.5–12.0:1 under full boost to keep the engine safe.
  • Dyno Tuning: A session on a chassis dynamometer provides precise data to dial in fuel maps and timing. Many 3000GT owners report peak gains of 40–50 whp on a 93-octane tune with the Greddy intercooler and supporting mods.

Never increase boost without verifying that your fuel system (injectors, fuel pump, and fuel pressure regulator) can deliver sufficient fuel. The 3000GT’s stock 450cc injectors are adequate for about 350 whp; beyond that, upgrades are needed.

Maintenance and Longevity

An intercooler is a relatively low-maintenance component, but a few practices will keep it performing optimally:

  • Keep the core clean: Bugs, oil residue, and road grime block airflow. Gently wash the fins with a low-pressure spray and a soft brush periodically.
  • Inspect connections: Silicone couplers can harden and crack over time. Check them annually and replace if they show signs of wear.
  • Check for boost leaks: A loose clamp or torn coupler will cause sluggish performance and high IATs. Re-test the system after any front-end work.
  • Protect against corrosion: Greddy cores are typically black powder-coated, but if you live in an area with road salt, consider applying a light coat of corrosion inhibitor on exposed aluminum brackets.

Cost-Benefit Analysis

A complete Greddy front-mount intercooler kit for the 3000GT typically costs between $800 and $1,200, depending on the specific version (e.g., standard core vs. larger “GT” core). Installation is a moderate DIY job; professional installation adds $300–$600. When combined with a tune ($300–$600), the total investment lands around $1,500–$2,000. For that price, you gain not only horsepower but also consistency and reliability — the ability to make multiple hard pulls on a hot day without the engine pulling timing. Compared to other power mods like upgraded turbos or a full exhaust, the intercooler offers one of the best horsepower-per-dollar improvements, especially on a boosted platform.

Conclusion

Upgrading to a Greddy intercooler on your Mitsubishi 3000GT addresses the vehicle’s most critical performance bottleneck: heat management. The installation, while requiring some mechanical patience, is well within the reach of a dedicated DIYer. The results — lower intake temperatures, stronger and more consistent power, and the ability to run higher boost safely — make it one of the most satisfying modifications for this iconic car. Combine the intercooler with a proper tune and you’ll unlock the true potential of the 6G72 twin-turbo engine. For more detailed information and community experiences, visit the 3S Garage / 3SI forums and the Greddy official website for product specifications.