The Real Cost of Building a 400 WHP Evo 9 with Forge Transmission Components

The Mitsubishi Lancer Evolution IX remains one of the most respected platforms in the performance car world. Its 4G63 engine, advanced all-wheel-drive system, and nimble chassis make it a favorite for enthusiasts chasing reliable four-digit horsepower. However, building a 400 wheel-horsepower (whp) Evo 9 that stays together on the street or track requires more than just a bigger turbo and a tune. The transmission, often overlooked in budget builds, becomes the weak link when torque spikes above stock levels. This guide provides a detailed cost breakdown for a 400 whp Evo 9 build centered around Forge transmission components, covering every major category from engine internals to labor.

Why 400 WHP Is the Sweet Spot for an Evo 9

Before diving into costs, it’s important to understand what 400 whp means for an Evo 9. The 2.0-liter 4G63 engine, with its cast-iron block and robust head design, is capable of handling 400 whp on stock internals if properly tuned. However, to achieve that power reliably and consistently, most builders opt for forged pistons, stronger connecting rods, and a turbo upgrade. At this power level, the Evo 9 retains excellent drivability, spools quickly with a suitable turbo, and remains relatively kind to the drivetrain—provided the transmission is strengthened. Below 400 whp, the stock five-speed gearbox can survive with careful driving; above it, failures become common. Forge Motorsport offers a range of transmission components specifically designed to handle the increased torque, making this build both reliable and cost-effective.

Engine Modifications: Building the Heart

The engine is the single largest expense in any 400 whp build. While the 4G63 is famously tough, upgrading the bottom end and breathing components is essential for longevity. Below is a breakdown of typical engine parts and their estimated costs.

Forged Pistons and Connecting Rods

Stock Evo 9 pistons are cast and can crack under sustained high boost and knock events. Forged pistons from brands like CP-Carrillo, Wiseco, or JE Pistons are necessary for a 400 whp target. Similarly, the stock rods are powdered metal and can bend under high cylinder pressure. Forged rods from Manley, Carillo, or Eagle are standard. Expect to spend around $1,200 to $1,500 for a set of pistons and rods.

Turbocharger Upgrade

The stock Evo 9 turbo (TD05HR-16G6) can be pushed to around 380 whp with supporting mods, but it becomes inefficient. A common upgrade is a Garrett GT3076R or a BorgWarner S256, which can comfortably support 450+ whp. A quality turbocharger kit, including manifold, wastegate, and lines, runs $1,500 to $2,500. Even a simple bolt-on upgrade like a FP Green or a Forced Performance HTA68 can hit 400 whp with proper tuning, costing around $1,400.

Intercooler and Intake System

A larger front-mount intercooler is mandatory to keep intake air temperatures in check. A quality unit from ETS, AMS, or Forge Motorsport will cost between $600 and $1,000. Additionally, a MAF housing delete, hard intake pipe, and blow-off valve are recommended. A boost controller and boost gauge add another $200.

Fuel System Upgrades

400 whp requires increased fuel flow. Stock fuel injectors (560 cc) are insufficient; injectors around 1000 cc are typical. A Walbro 450 or AEM 340 lph fuel pump is also necessary. Budget $400 to $700 for injectors and pump. A fuel pressure regulator and lines may add another $300.

ECU Tuning

You cannot build 400 whp without proper engine management. The Evo 9 uses a Mitsubishi ECU that can be flashed via ECUTek or Cobb Accessport (fewer options). Standalone ECUs like Haltech, MoTeC, or AEM are also popular. Tuning by a reputable shop costs $500 to $1,500 depending on dyno time and complexity.

Supporting Mods

These include a 3-inch turbo-back exhaust ($600–$1,200), upgraded intercooler piping ($200), oil cooler ($300), and possibly a new radiator ($400). Gaskets, fluids, and maintenance parts (timing belt, water pump, spark plugs) add another $500.

Total engine modification estimate: $4,500 – $7,500

The Transmission: Why Forge Components Matter

The stock Evo 9 five-speed transmission is known for its weakness: second gear and the center differential. At 400 whp, aggressive launches and shifts can strip gear teeth or snap shift forks. Forge Motorsport produces high-quality gearbox rebuild kits, clutch systems, and shifter components designed to handle exactly this power level. Here’s the breakdown.

Forge Gearbox Rebuild Kit

Forge offers a complete gearbox rebuild kit that includes bearings, synchros, seals, and gaskets. More importantly, they also sell upgraded gear sets (e.g., straight-cut gears or stronger helical gears) for the Evo 9. For a 400 whp street car, a full rebuild using Forge’s heavy-duty bearings and synchros is recommended. Cost: $1,000 – $1,800 depending on whether you choose the basic rebuild kit or add stronger gears. If you need to replace second gear with a billet unit, add $400–$600.

Forge Clutch Kit

The stock clutch will slip almost immediately at 400 whp. Forge’s clutch kit options include organic disc (street friendly) and sintered/ceramic puck (track use). A twin-disc setup offers the best balance, but a single-plate Kevlar or carbon disc can hold the power with a heavier pedal. Prices range from $600 to $1,200. A lightweight flywheel from Forge is another $400.

Forge Short Shifter

To improve shift feel and reduce slop, a Forge short shifter (around $300) is a worthwhile upgrade. It doesn’t add power but gives you more confidence when rowing through gears at high rpm.

Additional Transmission Items

A transmission cooler (about $250 by Setrab or Earl’s) helps extend gearbox life, especially if you track the car. Upgrading the center differential with a stronger unit (from Shep, Jack’s, or Forge) may be necessary if you plan on drag launches. That can cost $800–$1,500.

Total transmission component estimate: $2,100 – $4,500

Labor Costs: Paying the Experts

Unless you’re a seasoned mechanic, installing a built engine and transmission requires professional labor. Rates vary by location; expect $100–$150 per hour. Below are typical labor charges for a 400 whp build.

Engine Removal and Installation

Removing and reinstalling the 4G63 is an 8–12 hour job. Add time for swapping pistons, rods, and timing components. Budget $1,500 – $2,500. If you ship the engine out for short-block assembly, that’s separate.

Transmission R&R and Rebuild

Pulling the transmission, installing the Forge rebuild kit, clutch, and flywheel, and reinstalling everything takes 6–10 hours. $1,000 – $1,500.

Turbo and Supporting Mods Installation

Mounting a new turbo, intercooler, exhaust, and fuel system can take 8–12 hours. $1,200 – $1,800. Dyno tuning is extra: $500 – $1,000.

Total labor estimate: $2,500 – $4,500

Total Cost Breakdown Summary

Below is a consolidated table of estimated costs. These are real-world figures based on 2025 pricing from reputable suppliers and shops. Prices can vary by region, part availability, and specific choices.

  • Engine modifications: $4,500 – $7,500
  • Transmission components (Forge): $2,100 – $4,500
  • Labor: $2,500 – $4,500
  • Additional parts (hoses, fluids, hardware): $500 – $1,000
  • Total budget range: $9,600 – $17,500

To hit a realistic target, plan for $14,000–$16,000 for a turnkey 400 whp Evo 9 with a robust Forge-equipped transmission. This is inclusive of contingencies for unexpected issues (e.g., worn syncros found during teardown).

Where to Save Money (and Where Not To)

Achieving 400 whp doesn’t require every upgrade on the market. Here are smart places to cut costs without sacrificing reliability.

  • Skip the billet transmission gears if you’re staying under 450 whp and don’t drag race. Forge’s rebuild kit with OEM-grade second gear can suffice.
  • Use a used core transmission for the rebuild. Many shops can supply a core for $300–$500.
  • Choose a journal-bearing turbo over a ball-bearing unit. A Garrett GT30R journal bearing costs ~$1,000 less.
  • DIY simpler jobs like intercooler piping, boost controller installation, and vacuum line routing.
  • Buy a tune file from a reputable remote tuner (e.g., English Racing) instead of a dyno session, saving $500–$1,000.

Never cheap out on: forged pistons, fuel pump, clutch, and a quality turbo. Those are the backbone of a reliable 400 whp build.

Real-World Challenges to Expect

Building any high-performance car comes with hidden costs and frustrations. Common issues with an Evo 9 at 400 whp include:

  • Heat soak: The engine bay is tight. A properly ducted intercooler and hood vents are recommended. Budget $200 for ducting.
  • Boost creep: With a larger turbo, you may need a boost controller and a wastegate porting. Additional $150–$300.
  • Axle shafts: Stock axles can twist under hard launches. Upgraded joints (e.g., Driveshaft Shop) add $1,500.
  • Clutch pedal feel: Aggressive clutches are heavy. Consider a hydraulic clutch slave kit ($150) to make it streetable.

Why Choose Forge Transmission Components?

Forge Motorsport has been a trusted name in performance parts for over 20 years. Their transmission components are engineered specifically for the Evo platform, using high-grade steels and precise manufacturing. Forge gearbox kits are designed to reduce noise while improving strength, and their clutches offer predictable engagement. Unlike generic parts, Forge components are tested on the Evo’s unique shifter linkage and synchro design, ensuring proper fitment. Visit Forge Motorsport’s official site for their complete Evo 9 catalog.

  • EvolutionM.net – The largest Evo forum with build threads and DIY guides.
  • English Racing – Well-known Evo tuners offering remote tuning and parts.
  • ShepTrans – Another trusted source for Evo transmission rebuilds and gears.

Final Thoughts

Building a 400 whp Evo 9 with Forge transmission components is an achievable goal for an enthusiast with a realistic budget. The key is to prioritize the drivetrain: a strong engine is useless if the transmission fails. By investing in Forge’s gearbox rebuild kit, clutch, and short shifter, you’ll create a car that can handle daily driving, backroad blasts, and the occasional track day without catastrophic failure. Plan to spend around $14,000–$16,000 for a complete, professionally built car that will reward you every time you press the throttle. And always remember: tune it safely, maintain it meticulously, and enjoy the legend that is the Evo 9.