The Mitsubishi Eclipse GSX: A Tuning Icon

The Mitsubishi Eclipse GSX, produced from 1990 to 1999, remains one of the most popular platforms for performance enthusiasts. Powered by the legendary 4G63T engine and equipped with a full-time all-wheel-drive system, this car offers a robust foundation for serious power upgrades. Whether you are building a street-driven sleeper or a dedicated track weapon, selecting the right performance parts is critical. This guide covers the top brands and components that have proven themselves in the Eclipse GSX community, with a focus on proven reliability and real-world performance gains.

Turbocharger Upgrades: Garrett, BorgWarner, and Precision

The turbocharger is the single most impactful upgrade for any GSX. The stock TD05H-14B or 16G turbos are capable but quickly become a bottleneck at higher power levels. Upgrading to a modern turbo from a trusted manufacturer can transform the car's responsiveness and top-end pull.

Garrett Motion

Garrett is the gold standard in turbocharging. Their GTX and G-series turbos are engineered for maximum efficiency and durability. For the Eclipse GSX, the Garrett GTX3076R Gen II is a popular choice for those targeting 500–600 wheel horsepower. The ball-bearing center cartridge reduces spool time significantly, while the billet compressor wheel offers superior airflow over traditional cast wheels. Garrett also offers direct-fit upgrade kits for the 4G63, simplifying installation.

  • GTX3076R Gen II: Ideal for street/strip use; spools quickly and supports over 600 hp.
  • GT3582R: A classic choice for high-horsepower builds; slightly slower spool but massive top-end potential.
  • G25-550: A newer option that combines modern aerodynamics with fast spool; suitable for 450–550 hp goals.

For more information on Garrett turbo options, visit their official site.

BorgWarner

BorgWarner EFR (Engineered For Racing) turbos are another top-tier choice for GSX owners. They feature a dual ball-bearing cartridge, integrated wastegate, and a titanium-aluminide turbine wheel for reduced inertia. The EFR 7064 and 8374 are common fits, offering excellent transient response and high efficiency. The integrated recirculation valve simplifies plumbing, and the ceramic coating helps manage under-hood temperatures.

Precision Turbo & Engine

Precision Turbo’s Gen 2 and Gen 3 series turbos are widely used in the DSM community. The 5858 Gen 2 is a favorite for those wanting quick spool with the ability to support 600+ hp. Precision’s billet wheels and journal-bearing designs are proven in both street and drag racing applications. They also offer complete turbo kits tailored for the 4G63 platform.

Exhaust Systems: HKS, GReddy, and Thermal R&D

A free-flowing exhaust is essential for unlocking turbo performance. The stock GSX exhaust is restrictive, especially the downpipe and catalytic converter. Upgrading to a full 3-inch turbo-back exhaust is a standard first step.

HKS Hi-Power Exhaust

HKS has been a staple in Japanese performance parts for decades. Their Hi-Power exhaust line for the Eclipse GSX features a straight-through design with a polished stainless steel muffler. The deep, aggressive tone is iconic among DSM enthusiasts. HKS exhausts are mandrel-bent for consistent diameter, reducing back pressure and improving throttle response. They also offer a Hi-Power Silent version for those who want performance with a subtler sound.

  • Materials: 304 stainless steel with mirror-polished finish.
  • Fitment: Direct bolt-on for 2G Eclipse GSX; compatible with most aftermarket downpipes.
  • Sound: Deep bass note without excessive drone.

GReddy

GReddy (Trust) is another Japanese powerhouse with an extensive catalog for the Eclipse. Their EVO 2 and Ti-C exhaust systems are popular. The EVO 2 features a dual-cannister design with a muffler that adjusts sound based on exhaust flow. The Ti-C (Titanium/Carbon) is lightweight and offers a unique tone. GReddy also manufactures downpipes and test pipes that pair perfectly with their cat-back systems.

Thermal R&D Exhaust

Thermal R&D is a smaller but highly respected manufacturer based in California. Their 3-inch stainless steel exhaust kit for the Eclipse GSX is known for perfect fitment and a clean, race-inspired note. Thermal uses a combination of straight-through mufflers and Helmholtz resonators to eliminate drone without sacrificing flow. Many owners prefer Thermal for a quieter cabin experience while still enjoying significant power gains.

Fuel System Upgrades: Walbro, FIC, and Injector Dynamics

As boost levels rise, the stock fuel system quickly runs out of capacity. Upgrading the fuel pump, injectors, and regulator is mandatory for any build over 400 horsepower.

Walbro Fuel Pumps

Walbro is the de facto standard for high-flow in-tank fuel pumps. The Walbro 450 LPH (F90000267) is a drop-in replacement for the Eclipse GSX. It supports up to 800 wheel horsepower on E85 with proper injectors. The pump features a reduced-height design for easier installation and includes a strainer. For those running pump gas or lower power levels, the Walbro 255 LPH is a cost-effective option yet supports 450–500 hp.

Fuel Injector Clinic (FIC)

FIC offers high-impedance injectors specifically designed for the 4G63. Their 1000cc, 1200cc, and 1450cc injectors are popular for street and race applications. FIC injectors are flow-matched and include the proper connectors for a plug-and-play install on the Eclipse GSX. They are compatible with standalone ECUs and OEM-style flash tuning.

Injector Dynamics

For serious builds, Injector Dynamics (ID) injectors like the ID1700X or ID2600X are the top choice. They feature a unique eight-hole disc design for superior atomization, improving power and drivability. ID injectors are fully compatible with ethanol blends and are often used in 1000+ hp setups.

Proper tuning is essential to safely increase power. The Eclipse GSX uses a Mitsubishi Electronic Control Unit (ECU) that can be reprogrammed via flash tuning or replaced with a standalone system.

ECMLink is the most popular tuning solution for DSMs. It allows direct, real-time control over the stock ECU via a cable and laptop software. ECMLink V3 provides full control over fuel, timing, boost control, and more. It is user-friendly and widely supported by the community. For most hobbyists, ECMLink is the best balance of cost and capability.

AEM Infinity

AEM Infinity is a powerful standalone ECU used in many high-horsepower GSX builds. It offers advanced features like closed-loop boost control, traction control, and data logging. Plug-in harnesses are available for the Eclipse, eliminating the need for splicing. AEM Infinity is ideal for those running large turbos, nitrous, or E85.

Haltech Elite

Haltech is another premium standalone option. Their Elite 1500 and 2500 ECUs provide immense flexibility and high-speed processing. Haltech offers a specific 4G63 adapter harness, making it a direct replacement. The Haltech NSP (Nexus Smart Phone) tuning app allows wireless adjustments from your phone.

Suspension and Handling: BC Racing, Tein, and Whiteline

With more power, the factory suspension becomes a weak point. Upgrading coils, bushings, and sway bars improves traction and cornering.

BC Racing Coilovers

BC Racing offers a range of adjustable coilovers for the Eclipse GSX. The BR Series features 30-way dampening adjustment, ride height adjustability, and pillow ball upper mounts. For stiffer driving, the ER Series adds inverted monotube dampers for better heat dissipation. BC Racing is known for providing a comfortable ride while maintaining impressive handling.

Tein

Tein is another leading suspension brand with many options for the Eclipse. The Tein Flex Z and Tein Street Advance offer ride height and dampening adjustments at a competitive price. Tein’s EDFC (Electronic Dampening Force Controller) allows on-the-fly adjustment from the driver’s seat, ideal for drivers who switch between street and track.

Whiteline Sway Bars and Bushings

Whiteline produces high-quality sway bars, end links, and polyurethane bushings specifically for the Eclipse GSX. Their adjustable sway bars allow fine-tuning of roll stiffness. Replacing factory rubber bushings with Whiteline’s polyurethane versions reduces slop and improves steering response. A full bushing kit from Whiteline is a worthwhile upgrade for any GSX that sees track days.

Intercooling and Induction: GReddy, Precision, and Dejon Tool

Efficient intercooling is critical for maintaining consistent power on boost. A larger front-mount intercooler (FMIC) is a common upgrade.

GReddy FMIC Kits

GReddy offers a bolt-on 24-core intercooler kit for the 2G Eclipse GSX. It includes all necessary piping, clamps, and a blow-off valve flange. The intercooler core is designed for minimal pressure drop and high thermal efficiency. GReddy’s kit retains the factory crash beam for structural integrity.

Precision Turbo Intercoolers

Precision Turbo manufactures bar-and-plate intercoolers that are race-proven. Their PTE6262 or PTE7480 intercooler cores are available in various sizes to fit different grille openings. Precision’s intercoolers feature cast end tanks for even airflow distribution. While not a kit, many custom fabricators use Precision cores for GSX builds.

Dejon Tool

Dejon Tool is a small business specializing in DSM induction pipes and intercooler piping. They offer silicone upper and lower intercooler pipes that replace the restrictive factory rubber boots. Dejon also manufactures a well-designed blow-off valve relocation pipe that cleans up the engine bay. Their products are made in the USA and fit the 4G63 perfectly.

Block and Head Upgrades: Manley, Wiseco, and ARP

For builds exceeding 500 wheel horsepower, upgrading the bottom end and valvetrain is necessary.

Manley Pistons and Rods

Manley Performance is a leading supplier of forged pistons and connecting rods for the 4G63. Their Manley Turbo Tuff pistons are available in 8.5:1 or 9.0:1 compression ratios, ideal for high boost. Manley rods are I-beam designs made from 4340 steel, capable of handling over 800 hp with proper tuning.

Wiseco Pistons

Wiseco offers forged pistons with a proprietary skirt coating for reduced friction. Their plasma-moly rings ensure a good seal. Wiseco pistons are a popular alternative to Manley, especially for budget builds. Pair them with Manley rods for a proven combination.

ARP Head Studs and Fasteners

ARP is the industry standard for high-strength fasteners. Upgrading to ARP2000 or L19 head studs is essential to avoid lifting the head under high boost. ARP also produces main studs, rod bolts, and flywheel bolts specifically for the 4G63. Their hardware is reusable and rated far above OEM.

Conclusion

Upgrading a Mitsubishi Eclipse GSX with the right performance parts transforms it from a capable sport coupe into a serious performance machine. Brands like Garrett, HKS, Walbro, ECMLink, BC Racing, and Manley have earned their reputations through decades of proven performance on DSMs. Whether you are adding a simple exhaust or building a 1000 hp monster, choose components from recognized manufacturers to ensure reliability and fitment. Always pair upgrades with proper tuning and supporting modifications to create a balanced, drivable car that retains its legendary status.