The 2G Mitsubishi Eclipse (1995–1999) is one of the most accessible platforms for enthusiasts chasing real, reliable horsepower. Whether you are driving a naturally aspirated 420A or the iconic 4G63 turbo, the aftermarket ecosystem is deep, proven, and filled with options that can net you 50+ wheel horsepower without rebuilding the engine. In this guide, we break down the top five modifications that deliver consistent, repeatable gains. Each upgrade is explained with real-world dyno data, installation tips, and supporting modifications you should consider to maximize performance and reliability.

1. Cold Air Intake (10–15 WHP)

A proper cold air intake is one of the simplest and most cost-effective upgrades for any 2G Eclipse. The factory airbox is restrictive, especially on turbo models where the inlet path is convoluted. Replacing it with a mandrel-bent aluminum tube and a high-flow conical filter reduces intake restriction and lowers intake air temperatures.

How It Works

The stock intake system draws warm air from inside the engine bay. A cold air intake relocates the filter into the front bumper area or behind the headlight, where ambient air is cooler and denser. Denser air contains more oxygen, which supports more complete combustion and, with proper tuning, additional power.

Expected Gains

  • 10–15 whp on turbo 4G63 models (with stock turbo)
  • 8–10 whp on naturally aspirated 420A models
  • Improved throttle response and a more aggressive intake sound

Brand Recommendations

  • Dejon Tool – Known for durable powder-coated pipes and integrated MAF adapters.
  • Injen – Offers a true cold air intake for the 420A that routes the filter into the bumper.
  • K&N – Always a safe choice; pair with an appropriate pipe kit.

Installation Tips

When installing, ensure the filter is securely mounted and shielded from road debris. On turbo cars, avoid pulling hot air from the radiator fan area. Use a heat shield or wrap the pipe with reflective tape. Be aware that removing the factory airbox will expose the mass airflow sensor (MAF) to turbulence – if you see erratic idle or lean codes, you may need to add a MAF screen or retune.

2. Performance Exhaust System (15–25 WHP)

On a turbocharged 2G Eclipse, the factory exhaust is one of the biggest bottlenecks. The stock downpipe is restrictive, and the catalytic converter has a small internal diameter. Upgrading to a full 3-inch turbo-back exhaust system can reduce back pressure, allowing the turbo to spool faster and the engine to breathe more freely.

Why 3 Inches?

For the 4G63, 3-inch exhaust is the standard for making serious power. It is not just about peak numbers – the reduction in back pressure also lowers exhaust gas temperatures (EGTs), which is critical when turning up the boost. For naturally aspirated 420A models, a 2.5-inch cat-back system is sufficient and will not kill low-end torque.

Expected Gains

  • 15–20 whp on turbo 4G63 with a full turbo-back (including downpipe and high-flow cat or test pipe)
  • 10–15 whp on naturally aspirated 420A with cat-back and header
  • Noticeable weight savings over the stock system

Component Breakdown

  • Downpipe: 3-inch stainless steel with a divorced wastegate path is recommended.
  • Cat-back: Look for mandrel bends and a high-quality muffler. Brands like Apexi or Dejon Tool offer 2G-specific systems.
  • Test pipe vs. high-flow cat: A test pipe is legal for off-road use only but flows best. A high-flow catalytic converter like the MagnaFlow 200-cell is a good middle ground.

Common Pitfalls

Aggressive exhaust systems can attract unwanted attention from law enforcement. On 1995–1996 models, removing the second O2 sensor will trigger a check engine light unless you use a spark plug defouler or tune it out. Be prepared for a raspy sound if you go cat-less – pairing a resonator with a quality muffler will keep the tone deep.

3. Boost Controller (20–30 WHP)

If you own a turbocharged 2G Eclipse, the single most effective way to unlock power is to increase boost pressure. The factory boost level on the 2G 4G63 is around 10–12 psi. With a good boost controller and the supporting mods (fuel pump, injectors, ECU tuning), you can safely run 18–20 psi on the stock turbocharger (T25 or 14B), yielding massive gains.

Manual vs. Electronic

  • Manual boost controller (MBC): Inexpensive, reliable, and simple. Adjusts boost by bleeding off pressure to the wastegate actuator. Best for a set-and-forget setup.
  • Electronic boost controller (EBC): More precise and allows you to run different boost levels for different gears or RPM ranges. Can also prevent boost spikes. Brands like GFB or HKS are popular.

Expected Gains

Raising boost from 10 psi to 18 psi on a 4G63 with a 14B turbo can produce 20–30 additional wheel horsepower. This is the biggest single-mods gain on this list, but it requires attention to fuel delivery and detonation control.

Critical Supporting Mods

  • Fuel pump: The factory fuel pump will struggle above 15 psi. Upgrade to a Walbro 255 lph high-pressure pump.
  • Injectors: Stock 450 cc injectors are fine up to about 16 psi on the 14B. Beyond that, step up to 550 cc or 650 cc injectors.
  • Wideband O2 sensor: Essential for monitoring air/fuel ratios when turning up boost.
  • Intercooler: The factory side-mount intercooler will heat-soak quickly. A front-mount intercooler (FMIC) is recommended for sustained boost runs.

Tuning Safety

Never increase boost without a method of adjusting fuel and ignition timing. Relying solely on the factory ECU will result in knock and possible engine damage. That leads directly to our next mod.

4. ECU Tune (15–25 WHP + Drivability)

The factory ECU on the 2G Eclipse is programmed conservatively for reliability, emissions, and fuel economy. A proper tune – whether via a reflash, a piggyback unit, or a standalone ECU – unlocks hidden power and ensures that your other modifications work in harmony. For turbo models, this is the gatekeeper to safe high-boost operation.

Tuning Options

  • ECMLink (formerly DSMlink): The gold standard for 1G and 2G DSMs. It allows real-time tuning of fuel maps, ignition timing, boost control, and more. It requires an EPROM ECU, but many 2Gs have them stock. Check your ECU code.
  • Standalone ECUs: AEM EMS, Haltech, or Megasquirt for maximum control. More expensive and requires advanced knowledge.
  • Piggyback chips: Older options like the SAFC (Super Air Fuel Controller) can adjust airflow readings for minor tuning but are less capable than modern solutions.

Expected Gains

  • 15–25 whp on a 4G63 with basic bolt-ons and a proper tune
  • Significantly improved throttle response and smoother idle
  • Custom launch control and anti-lag features (with ECMLink)

DIY vs. Professional

Getting a base tune from a reputable DSM tuner is highly recommended. A poor calibration can lead to detonation and failure. Many shops offer mail-in tunes if you have the right hardware. After the base tune, you can learn to tweak the maps yourself using the vast resources on ECMLink forums.

5. Lightweight Flywheel (5–10 WHP + Acceleration)

While a lightweight flywheel does not increase peak engine horsepower, it reduces rotating mass, which frees up horsepower that was otherwise lost to accelerating the flywheel itself. This translates to quicker revs and faster acceleration in every gear. On a 2G Eclipse, switching from a stock 23-pound flywheel to an 11–14 pound unit is one of the best drivability upgrades you can make.

Material Choices

  • Chromoly steel: Durable and street-friendly. Offers a 40–50% weight reduction without excessive chatter.
  • Aluminum: Even lighter, but requires a steel wear surface and can cause more transmission noise at idle.
  • Billet steel: The heaviest of the aftermarket options, but still much lighter than stock.

Expected Gains

  • Dyno proven 5–10 whp gains at higher RPM due to reduced drivetrain loss
  • Faster engine rev-match during downshifts
  • Noticeable improvement in 0–60 times

Installation Notes

Replacing the flywheel requires removing the transmission, so it is best done alongside a clutch upgrade. For boosted applications, pair the flywheel with a performance clutch (e.g., ACT, South Bend, or Competition Clutch) that can handle increased torque. Use new pilot bearing and throwout bearing. A lightweight flywheel may cause a slight increase in gear rattle at idle – this is normal and not a sign of damage.

Putting It All Together: The 50+ WHP Recipe

To reach the 50+ wheel horsepower goal, you do not need each mod to be maxed out. A typical budget build might include:

  • Cold air intake – 10 whp
  • Turbo-back exhaust – 15 whp
  • Boost controller @ 16 psi – 20 whp
  • Lightweight flywheel – 5 whp

This combination nets about 50 whp on a 4G63 with no internal engine modifications. Adding an ECU tune and proper fuel upgrades will allow you to push past 15 psi safely and exceed 60 whp gains. Remember that dyno numbers vary by weather, altitude, and dyno type – focus on the percentage improvement and driving feel.

Supporting Mods You Shouldn't Ignore

To keep your newly powered Eclipse reliable, consider these supporting modifications:

  • Fuel pump rewire: Reduce voltage drop to the pump for consistent fuel pressure.
  • Upgraded intercooler: A front-mount intercooler prevents heat soak and allows higher boost without detonation.
  • Catch can: Reduces blow-by in the intake tract, important when boost is raised.
  • Better cooling: A Mishimoto or Koyo aluminum radiator helps manage the extra heat from increased power.

Final Thoughts

The 2G Eclipse platform rewards smart, sequential modifications. The five mods listed here – intake, exhaust, boost control, ECU tuning, and a lightweight flywheel – form a proven path to a reliable 50+ horsepower increase. Always prioritize tuning and fuel delivery before turning up the wick. With the right parts and patience, your Eclipse will transform from a daily driver into a serious street performer.

For further reading and community support, check out DSMtuners.com, a decades-old resource for 1G/2G DSM enthusiasts. You can also find technical articles and parts at Dejon Tool and tuning guides at ECMTuning.