Why the Exedy Stage 1 Clutch Is a Game-Changer for Your Evo

Tuning a Mitsubishi Lancer Evolution is more than just bolting on a bigger turbo or flashing a new ECU map. When you start pushing the 4G63 or 4B11T engine beyond stock levels, the drivetrain becomes the bottleneck. One of the earliest and most impactful upgrades you can make is the clutch. The Exedy Stage 1 Clutch has earned a reputation as a reliable, street-friendly upgrade that can unlock significant power gains—up to 50 horsepower. But how does a clutch actually “add” horsepower? In this article, we break down the engineering, real-world benefits, installation process, and supporting modifications that make this upgrade a cornerstone of any Evo tuning project.

Understanding the Exedy Stage 1 Clutch

Exedy (formerly Daikin) has been a leading OEM and aftermarket clutch manufacturer for decades. Their Stage 1 clutch is specifically designed for cars making moderate power increases—typically up to around 400 wheel horsepower for an Evo VIII, IX, or X. Unlike a stock clutch, which uses organic friction materials with limited heat tolerance, the Stage 1 employs a high-performance organic / Kevlar hybrid friction facing that provides a significant increase in torque capacity without the aggressive engagement of a puck-style or ceramic clutch.

Construction and Materials

The pressure plate uses a heavy‑duty diaphragm to increase clamping force by 20‑30% over stock, while the disc features a reinforced hub and spring‑centered design to dampen driveline shock. This reduces the risk of chattering while still handling the extra thermal load from repeated launches. The result is a clutch that feels nearly as smooth as the factory unit but can hold substantially more torque.

  • Torque capacity: Approximately 400-450 lb-ft at the crank (versus ~300 lb-ft for stock)
  • Friction material: High‑organic / Kevlar blend – offers good pedal feel and low wear rates
  • Warranty: Exedy provides a limited manufacturer warranty on materials and workmanship

How It Differs from a Stock Clutch

Factory Evo clutches are designed to last 60,000+ miles under normal driving. They use a soft organic friction disc and a pressure plate with modest clamping force. Under the increased boost and torque from a tune, the stock clutch begins to slip, especially in higher gears or during aggressive acceleration. This slip wastes energy—energy that could otherwise turn the wheels. The Exedy Stage 1 eliminates that slip, allowing the engine’s full output to reach the transmission.

Does the Clutch Really Add 50 Horsepower?

There is a common misconception that swapping a clutch directly increases engine output. The engine itself does not gain any extra horsepower from a clutch change. However, a clutch upgrade can unlock horsepower that is otherwise lost through drivetrain slip and heat dissipation. Here’s how the 50‑hp gain comes about:

Reducing Drivetrain Loss

When a stock clutch slips under high torque, the engine’s power does not all reach the wheels—some is converted to heat in the friction disc. By eliminating that slip, the Exedy Stage 1 reduces parasitic power loss. Independent dyno tests have shown that an Evo with a slipping stock clutch may see a gain of 15–25 wheel horsepower simply by installing a stronger clutch that holds WOT pulls without slip.

Enabling a More Aggressive Tune

The bigger picture is that a Stage 1 clutch allows you to run a more aggressive ECU tune. With the stock clutch, tuners often have to limit throttle ramp rates or dial back boost in the midrange to avoid clutch slip. Once you have a clutch that can handle the torque, the tuner can safely increase boost, advance timing, and lean out the air‑fuel mixture. This is where the remaining 25–30 of the advertised 50 hp comes from. The combination of reduced slip and a bolder tune results in a net gain of approximately 50 horsepower at the wheels on a stock‑frame turbo Evo.

“On a Stage 1 tune with supporting mods, the Exedy Stage 1 clutch consistently allows us to dial in another 3-4 psi of boost without slipping. That’s a solid 30-40 whp over the same setup with a stock clutch.” — Professional tuner from an Evo specialty shop

Real-World Dyno Results

We’ve compiled data from several well‑known Evo tuning forums (like EvolutionM.net and the UK Lancer Register) showing that an Evo IX with full bolt‑ons — intake, exhaust, intercooler, fuel pump, and a conservative pump‑gas tune — often makes 320–340 whp on a DynoJet. After swapping the stock clutch for an Exedy Stage 1 and re‑tuning, the same car easily hits 370–390 whp. That’s a consistent 40–50 whp gain directly attributable to the clutch upgrade and accompanying tune.

Benefits Beyond Horsepower

While the headline‑grabbing number is 50 hp, the Exedy Stage 1 offers numerous other advantages that make it a smart investment for daily drivers and weekend track warriors alike.

Improved Acceleration and Throttle Response

The lightweight disc (approx. 10% lighter than stock) reduces rotational inertia. This means the engine revs more freely during shifts, and the drivetrain feels more responsive. Combined with a lightweight billet flywheel (optional but recommended), the Stage 1 clutch makes the Evo feel snappier in every gear.

Consistent Engagement

Friction fade is a common issue with organic clutches during repeated hard launches. The Exedy Stage 1’s material is designed to handle higher operating temperatures before fading. The result: consistent engagement even after several pulls or a session on a road course. This reliability builds driver confidence.

Future‑Proofing for Mods

Even if you’re not currently maxing out your stock frame turbo, the Exedy Stage 1 leaves headroom for future upgrades—such as a bigger turbo, cams, or E85 fuel. You won’t have to pull the transmission again just because you added 50 more horsepower down the road.

Installation Guide: What You Need to Know

Installing a clutch on an Evo is a moderate‑to‑difficult job that requires a solid weekend, a good set of tools, and a transmission jack. If you’re not comfortable pulling the transfer case and transmission, a shop will typically charge 8‑12 hours of labor (~$800–$1,200). For DIY installers, here are critical considerations:

Tools and Supplies Required

  • Floor jack and four strong jack stands
  • Transmission jack or a sturdy floor jack with a transmission adapter
  • Metric socket set (including 10, 12, 14, 17, 19, and 22 mm)
  • Torque wrench (0‑250 ft‑lb range)
  • Clutch alignment tool (usually included with the Exedy kit)
  • Flywheel bolts (new recommended) and 6‑point socket
  • High‑temperature grease for the pilot bearing and splines
  • PB Blaster or other rust penetrant for exhaust bolts

Flywheel Considerations

Most Evo owners opt to replace the flywheel when doing a clutch job. The stock flywheel is a dual‑mass unit that can be heavy (around 22 lbs) and sometimes suffers from failure of the internal springs. Exedy offers a lightweight single‑mass flywheel (about 13 lbs) that works perfectly with the Stage 1 clutch. It reduces rotational mass, improving throttle response and making rev‑matching easier. However, it may introduce a slight gear rattle at idle. If you prefer a more OEM‑like experience, you can keep the stock flywheel and have it resurfaced — just make sure the step height remains within specification (typically 0.020‑0.025 inches).

Step‑by‑Step Installation Overview

  1. Disconnect the battery and remove the air intake assembly for access.
  2. Drain the transmission and transfer case oil.
  3. Support the engine with a jack under the oil pan (use a block of wood to prevent damage).
  4. Remove the transfer case, then the starter motor, and finally the transmission.
  5. Unbolt the pressure plate and clutch disc from the flywheel.
  6. Remove the flywheel (pay attention to the orientation of the dual‑mass bolts).
  7. Install the new flywheel (if applicable) and tighten to 95 ft‑lb using new flywheel bolts.
  8. Apply a very thin layer of high‑temp grease to the transmission input shaft splines.
  9. Align the new disc using the alignment tool, then install the pressure plate and tighten bolts in a star pattern to 22 ft‑lb (check Exedy spec).
  10. Re‑install the transmission, transfer case, and all accessories. Refill fluids with high‑quality gear oil.
  11. Pump the clutch pedal 20‑30 times before starting the engine to bleed any air from the hydraulic system.

Break‑In Procedure (Crucial for Longevity)

Most clutch manufacturers recommend a 500‑mile break‑in period. During this time you should avoid full‑throttle launches, excessive slipping, and long periods of holding the clutch at the friction point (e.g., parking on a hill by riding the clutch). Drive gently for the first 200 miles, then gradually increase load. The goal is to allow the friction material to transfer evenly onto the flywheel surface. Skipping the break‑in can cause glazing and premature failure, reducing the clutch’s clamping capacity.

Supporting Modifications to Maximize the 50‑Hp Gain

The Exedy Stage 1 clutch alone won’t magically increase power; you need supporting modifications that allow the engine to produce more torque without slipping. Here’s a typical “Stage 1” package for an Evo:

ECU Tuning (Custom or Off‑the‑shelf)

A proper tune is the most important companion to a clutch upgrade. Many tuners use ECUFlash or COBB AccessPORT to reprogram the factory ECU. With the clutch now able to hold the torque, the tuner can raise boost targets, adjust ignition timing, and calibrate the fuel maps. Expect a gain of 30‑50 hp from tuning alone on a stock frame turbo (such as the Evo IX’s 9.8T or the Evo X’s MHI TF06).

Fuel System

To support higher boost and increased fueling, a 255‑300 LPH fuel pump (e.g., Walbro 255 or Aeromotive Stealth) is standard. On Evo X cars, a flex‑fuel sensor and larger injectors (1000 cc or more) are common if running E85.

Intake and Exhaust

Freeing up airflow is essential. A drop‑in filter or cold‑air intake, along with an upgraded intercooler (ETS or AMS), reduces intake temperatures. A cat‑less downpipe and an exhaust system with 3‑inch piping significantly reduce backpressure, allowing the turbo to spool faster and hold higher boost levels.

Drivetrain Upgrades

Once the clutch can handle the torque, the next weak link is often the stock transmission. While the Evo’s 5‑ or 6‑speed gearbox is robust, a shifter bushing kit and upgraded engine/transmission mounts will improve shift feel and reduce driveline slop. Some owners also install a Cusco or Kaaz 1.5‑way limited‑slip differential to better put down the extra power.

Common Mistakes and Pitfalls

  • Not replacing the pilot bearing: Always install a new pilot bearing when doing a clutch. A worn bearing can cause vibration and premature failure.
  • Skipping the flywheel resurface: Even if you keep the stock flywheel, resurfacing it is critical for proper disc mating. A glazed or stepped flywheel will cause chatter and slipping.
  • Over‑greasing the splines: Too much grease can contaminate the disc. Use only a light film.
  • Rushing the break‑in: A weekend track day right after installation can ruin the clutch. Be patient.
  • Ignoring hydraulic system air: If the pedal feels spongy after installation, bleed the system. Air can cause incomplete disengagement and grinding into reverse.

To help you plan your upgrade, here are trusted sources for parts and technical information:

Frequently Asked Questions

Will the Exedy Stage 1 clutch make my daily driving harsh?

No. The Stage 1 is often described as “near‑stock” in pedal effort. The organic/kevlar material engages smoothly, and there is no on‑off switch effect like a puck clutch. It is perfectly livable for stop‑and‑go traffic.

How long does the Exedy Stage 1 last?

With proper break‑in and street driving, expect 40,000‑60,000 miles. Track use and hard launches will shorten that lifespan. The disc wears faster than the pressure plate, but the kit is generally durable.

Can I use the Exedy Stage 1 clutch with a twin‑disk system later?

If your power goals exceed 500 whp (e.g., a built engine with a GT35R turbo), you may eventually outgrow the Stage 1. But for a typical upgraded stock‑frame turbo Evo (up to 450 whp), the Stage 1 is more than adequate.

Do I need to replace the slave cylinder?

Not necessarily, but if it shows signs of leaking or has high mileage, it’s cheap insurance to replace it while the transmission is out. Also check the clutch fork and pivot ball.

Conclusion

The Exedy Stage 1 clutch is one of the highest‑value upgrades you can make to a Mitsubishi Lancer Evolution. It does not create horsepower by itself, but it eliminates the drivetrain losses that rob power, and it enables a more aggressive tune that can add a genuine 50 horsepower over a stock clutch. Combined with proper supporting modifications and careful installation, this clutch will transform your Evo’s responsiveness, reliability, and overall driving experience. Whether you’re a weekend track warrior or a daily driver who loves a little more performance, the Exedy Stage 1 is a proven path to unlocking your car’s full potential.

Ready to upgrade? Grab the kit, schedule the install, and give your Evo the clamping force it deserves. Your right foot — and your dyno sheet — will thank you.