Understanding the Eclipse GSX Upgrade Path

The Mitsubishi Eclipse GSX, equipped with the legendary 4G63T engine and a robust all-wheel-drive system, remains one of the most tunable platforms in the automotive world. Whether you’ve just picked up a stock example or are looking to breathe new life into a project car, understanding upgrade costs is essential to building a reliable, fast machine. The price spectrum is wide: you can start with a basic intake and exhaust for around $1,200 or go all-in with a full turbo build costing $5,000 or more. Your final bill depends heavily on parts quality, new vs. used sourcing, and whether you turn wrenches yourself or pay a shop. Below we break down each upgrade tier, from simple bolt-ons to thorough internal engine builds.

Basic Intake and Induction Upgrades

The easiest way to improve throttle response and let the 4G63 breathe is with an upgraded intake system. A basic package—cold air intake, high-flow air filter, and maybe a ported intake manifold—typically starts around $1,200 if you buy new parts and do the work yourself. Here’s what you’re looking at:

  • High-Flow Air Filter Kit (cold air or short ram): $100–$300. Brands like K&N, AEM, or Injen drop right in and flow significantly better than the restrictive factory airbox.
  • Upgraded Intake Manifold: $800–$1,000 for a cast aluminum unit from Magnus, FFWD Connection, or equivalent. Porting your stock manifold is cheaper ($200–$400) but yields less gain.
  • Throttle Body Upgrade: $150–$300. A 60mm or 65mm throttle body from a 3000GT VR-4 or aftermarket unit improves airflow into the manifold.

Many owners stop here and enjoy a noticeable gain in top-end power. For parts sourcing, check ExtremePSI, a longtime vendor for DSM and Evo components. For DIY tips, DSM Tuners offers a wealth of build threads and part reviews.

Exhaust System Upgrades for the Eclipse GSX

Freeing up the exhaust side is the next logical step after improving intake flow. A full turbo-back exhaust system—downpipe, high-flow catalytic converter (or test pipe), and cat-back—typically costs $800–$1,200 for quality stainless steel parts from brands like HKS, Apexi, or Megan Racing. Individual components:

  • Downpipe: $200–$400. A 3-inch downpipe eliminates the restrictive factory piece and reduces backpressure.
  • High-Flow Cat or Test Pipe: $100–$250.
  • Cat-Back Exhaust: $400–$600. Choose a dual-tip or single muffler design based on sound preference.

Pair the exhaust with a ported exhaust manifold (often included in a turbo kit, but a stock manifold can be ported for $100) for additional flow. A good exhaust setup combined with the intake upgrade easily costs around $2,000 total but transforms the car’s responsiveness.

Mid-Level Performance Upgrades: Turbo, Fuel, and Cooling

Once you’ve handled breathing, the real performance gains come from upgrading the turbocharger, fuel system, and intercooling. This tier typically runs between $2,500 and $3,500 for parts alone, not including tuning or labor. Here’s the breakdown:

Turbocharger Upgrade

  • Evo III 16G Turbo: $1,000–$1,500. This is the most popular bolt-on upgrade for the GSX, supporting 350–400 hp with proper fuel and tuning. New units from MHI or rebuilt cores are available.
  • FP Big T28 or Garrett GT series: $1,200–$1,800 for higher-flow options that support 450+ hp.

Fuel System Upgrades

  • High-Flow Fuel Pump: $100–$200. A Walbro 255 lph pump is standard; for big power go with a 450 lph unit.
  • Upgraded Fuel Injectors: $500–$800 for a set of 750cc to 1000cc injectors (e.g., FIC, Injector Dynamics).
  • Adjustable Fuel Pressure Regulator (AFPR): $150–$300. Essential to maintain correct fuel pressure under high flow.

Intercooler and Charge Air System

  • Front Mount Intercooler (FMIC) Kit: $400–$800. A larger core reduces intake air temperatures significantly. Brands like VRSF or spearco make direct-fit kits for the GSX.
  • Short Route Piping Kit: $200–$400.

Boost Control and Engine Management

  • Manual Boost Controller: $30–$100. Simple, but a reliable electronic boost controller (like a TurboXS or AEM) costs $150–$300.
  • Engine Management (ECU tuning): $500–$1,000 for a standalone ECU (e.g., AEM EMS, Link G4+, or ECMLink). ECMLink is the community favorite for the 1G/2G DSM.

For sourcing, STM Performance stocks many of these parts. Tuning advice can be found on DSM Tuners forums under the “Tuning and Engine Management” section.

Full Turbo Build: Maximum Power on a Budget

For serious power—400 hp and beyond—a full turbo build replaces not just the turbo but also the engine internals, transmission, and clutch. Total cost typically hits $5,000 for parts only, with labor and tuning adding another $2,000–$3,000. Here’s what a comprehensive build includes:

Turbo Kit and Manifold

  • Complete Turbo Kit: $2,500–$3,500. This includes a large-frame turbo (Garrett GT35R, BorgWarner SXE series), tubular manifold, wastegate, blow-off valve, and all gaskets/fittings. A quality kit from MAPECU or Forced Performance is recommended.

Upgraded Engine Internals

  • Forged Pistons and Connecting Rods: $800–$1,500 for a set from Wiseco, JE Pistons, or Manley. Stock pistons are safe up to about 400 hp; beyond that, forged units are mandatory.
  • Head Studs and Main Studs: $150–$300. ARP studs are the standard.
  • Performance Camshafts: $400–$800. Kelford, GSC, or HKS cams with upgraded valve springs and retainers.
  • Head Gasket and Timing Belt: $200–$400. Use a multi-layer steel (MLS) head gasket and a Gates Racing timing belt.

Fuel System for High Horsepower

  • Dual In-Tank Fuel Pumps or External Pump: $400–$800.
  • Larger Injectors: $600–$1,000 for 1600cc or bigger injectors if running E85.
  • Fuel Rail and Lines: $200–$500.

Drivetrain Upgrades

  • Clutch: $400–$800. A twin-disc clutch from South Bend or ACT is needed for 450+ hp.
  • Transmission Rebuild or Upgrade: $1,000–$2,500. The stock 5-speed can be strengthened with shot-peened gears, a welded center differential, or a full stage-2 build from Jacks Transmissions.

A full build like this is not a weekend job for most owners. Expect to invest significant time in assembly and tuning. Many choose to have a shop do the engine and transmission work, which can double the budget.

Tuning and Labor Costs

No matter which upgrade path you choose, tuning is what ties everything together. An untuned car with upgraded parts will run poorly and potentially damage the engine. Here are the typical costs:

  • Dyno Tuning (professional session): $500–$1,000 per session, depending on the tuner and region. Reputable shops like English Racing (in Washington) or Curt Brown (ECMLink specialist) charge premium rates but deliver safe, reliable tunes.
  • ECU Flash or Chip Tuning (mail-order): $200–$500 if you already have an ECU with a flashable socket (e.g., ECMLink chip).
  • Labor for installation: $100–$150 per hour at most shops. A basic intake and exhaust install might take 4–6 hours; a full turbo build can take 30–60 hours.

DIY work can save you $1,000–$2,000, but it requires mechanical skill, proper tools (engine hoist, torque wrench, dial gauge), and a clean workspace. If you’re new to the platform, start with simple bolt-ons and learn the car before tackling internals.

Additional Considerations: Reliability, Hidden Costs, and Used Parts

Upgrading a GSX isn’t just about buying parts. The car is over 20 years old, so you’ll likely face unexpected maintenance. Factor these into your budget:

  • Timing Belt and Water Pump Replacement: Every 60,000 miles, but a high-performance build that stresses the engine may require more frequent changes. Parts and labor: $600–$1,000.
  • Head Gasket Failure: Common when pushing stock boost above 16 psi. Upgrading to an MLS gasket and ARP studs early is cheap insurance.
  • Crank Walk or Oil Pump Issues: The 4G63 7-bolt engine (1992–1999 GSX) is prone to crank walk if oiling is neglected. Install a new or upgraded oil pump ($200–$400) and a balance shaft elimination kit ($150).
  • Cooling System Upgrades: After a large turbo and FMIC, the stock radiator struggles. A Mishimoto or Koyo radiator costs $300–$500.
  • Transmission Weaknesses: The stock 5-speed will break above 400 hp. Factor in a rebuild or swap to a ShepTrans or Jacks stage-2 unit.

Used parts can save money, but be cautious: a used turbo may need a rebuild ($200–$400), and old wiring harnesses are brittle. Forums like DSM Tuners and Facebook groups (DSM Classifieds) are good places to find deals, but inspect everything.

Conclusion: Build Smart, Spend Wisely

Upgrading a Mitsubishi Eclipse GSX is an addictive journey that can reward you with a thrilling driving experience. Whether you aim for a reliable 300 hp daily driver or a 500+ hp weekend warrior, your budget will dictate the path. A basic intake and exhaust setup costs around $1,200 and wakes up the car without breaking the bank. Mid-level builds with a bigger turbo, fuel system, and intercooler run $2,500–$3,500. Full builds that include forged internals, a massive turbo, and a built transmission can easily top $5,000 for parts alone. Remember to set aside money for tuning and unexpected repairs—your build’s reliability depends on it. Use resources like DSM Tuners and ExtremePSI to research parts and prices, and never skip the dyno tune. With careful planning and a realistic budget, you can build a GSX that rivals modern sports cars for a fraction of the price.