Introduction: The AMS 20G Turbo for the Mitsubishi Evo

The Mitsubishi Lancer Evolution—often called the Evo—has earned a legendary reputation among performance car enthusiasts. Its rally-bred all-wheel drive, high-revving 4G63 engine, and robust turbocharging system made it a tuner favorite from the factory. But as with any iconic platform, the quest for more power never stops. The AMS 20G turbocharger is one of the most well-regarded bolt-on upgrades for the Evo, offering a significant jump in horsepower while retaining good street manners. This performance breakdown examines exactly how much power the AMS 20G adds, what supporting modifications are required, and how the upgrade transforms the driving experience.

AMS Performance (now part of the EVOMS group) engineered the 20G turbo specifically for the Evo’s 4G63 engine. It uses a 20G compressor wheel, a larger turbine housing compared to the stock TD05, and an upgraded center section. The result is a turbo that can flow substantially more air than the factory unit, supporting power levels well beyond 400 wheel horsepower (whp) with proper tuning. But numbers alone don’t tell the full story—the real-world performance delta, spool characteristics, and reliability are equally important. We’ll break down every aspect so you can decide if the AMS 20G is right for your build.

Understanding the AMS 20G Turbo: Specifications and Design

To appreciate the power gains, it helps to know exactly what the AMS 20G offers compared to the stock Evo turbo. The factory turbo on most Evos (Evo VIII/IX) is a Mitsubishi TD05HR with a 16G compressor wheel. The “16G” refers to the size of the compressor wheel’s inducer diameter in millimeters. The AMS 20G steps up to a 20G wheel, which is significantly larger.

Key Specifications

  • Compressor Wheel: 20G billet (or cast, depending on revision) with a 53mm inducer and 76mm exducer (approximate), compared to the stock 16G’s 49mm inducer.
  • Turbine Wheel: Upgraded TD06 or TD07 turbine (depending on setup), often with a larger 7–8 cm² turbine housing to reduce exhaust backpressure at high boost.
  • Boost Capability: Safely supports 30–35 psi with proper tuning, though most street setups run 25–28 psi on pump gas.
  • Airflow: Approximately 45–50 lb/min, compared to the stock 16G’s 40–42 lb/min. This extra airflow is the primary source of power gain.

The AMS 20G is typically available as a “bolt-on” upgrade, meaning it can use the stock manifold, oil lines, and coolant lines with minimal modification. Some kits include a new dump pipe or require slight porting to the stock exhaust manifold to match the larger turbine inlet. It’s a straightforward upgrade for those with moderate mechanical skills.

Power Gains: How Much Horsepower and Torque Can You Expect?

The headline number: with proper tuning and supporting mods, an Evo equipped with an AMS 20G turbo typically makes between 380 and 420 whp on pump gas (91–93 octane). On race gas or E85, results can push past 450 whp. Torque often climbs to 350–400 lb-ft at the wheels. Compared to a stock Evo VIII/IX (approximately 250–270 whp on a dynojet), that’s a gain of 120–170 whp—a massive increase for a simple turbo swap.

However, these numbers depend heavily on the supporting modifications. A stock Evo with a bolt-on AMS 20G and nothing else will not hit 400 whp; the turbo will be starved for fuel and airflow. The realistic baseline for the AMS 20G is a “stage 2” setup: upgraded fuel pump, larger injectors (850–1050 cc), a good intercooler, a full 3-inch exhaust, and a quality tune (via ECUFlash or a standalone ECU). With that configuration, most owners report 380–400 whp on pump gas. Add cams, a ported head, and a larger intake manifold, and 440+ whp is achievable.

  • Stock 16G: 250–300 whp (depending on year)
  • FP Green (a similar sized upgrade): 380–430 whp
  • AMS 20G: 380–450 whp
  • Precision 5858 (larger, slower spool): 450–550 whp

The AMS 20G occupies a sweet spot—it provides near-FP Green power but often spools slightly faster due to its smaller turbine housing options. Many enthusiasts find it the ideal turbo for a strong street car that can still track or autocross.

Factors That Influence Actual Power Output

No two Evos are identical, and the AMS 20G’s power output varies based on several critical factors. Understanding these will help you set realistic expectations and avoid disappointment.

1. Tuning Quality

This is the most important variable. A skilled tuner can extract every last horsepower from the AMS 20G while keeping the engine safe. Poor tuning can leave 30–50 hp on the table or, worse, cause detonation and engine failure. Always seek a tuner experienced with Evo ECUs and the AMS turbo platform.

2. Fuel Choice

Pump gas limits boost due to knock. E85 (ethanol) is the gold standard for high-boost applications—it cools the intake charge and allows more aggressive timing. With E85 and the AMS 20G, you can safely run 28–30 psi and achieve 420+ whp. Race gas (100+ octane) offers similar benefits but at a higher cost.

3. Supporting Modifications

The stock Evo fuel system maxes out around 350 whp. To support the AMS 20G, you need at least a Walbro 255 or 450 lph fuel pump and 850 cc injectors. Intake and exhaust restrictions also matter: a stock airbox and restrictive exhaust can choke the turbo. A 3-inch downpipe and cat-back, along with a high-flow intake (like an AEM or HKS), are highly recommended.

4. Intercooling Efficiency

The stock Evo intercooler (especially on the VIII) is adequate for the 16G but becomes a heat soak liability above 350 whp. Upgrading to a larger bar-and-plate front-mount intercooler (e.g., AMS, ETS, or Garrett core) reduces intake temperatures by 20–40°F, allowing more boost without detonation.

5. Engine Health and Compression

An engine with lower compression (due to mileage or wear) cannot make as much power. A fresh 4G63 with proper ring seal and valve condition will produce the best results. Also, consider upgrading the head studs to ARP L19s; the added cylinder pressure from the 20G can lift the head on high-mileage stock studs.

Performance Benefits Beyond Raw Horsepower

The AMS 20G improves more than just peak power numbers. The enhanced area under the power curve—especially in the mid-range—transforms the driving experience.

Improved Boost Response

Thanks to the billet compressor wheel and optimized aerodynamics, the AMS 20G spools nearly as quickly as the stock 16G. Full boost (around 25 psi) arrives by 3500–3800 rpm on a properly tuned car. This is only 200–300 rpm later than stock, yet the turbo makes substantially more torque at the same engine speed. The result is a punchy, responsive engine that doesn’t feel laggy.

Higher Top-End Power

While the stock 16G runs out of breath near 6500 rpm, the AMS 20G pulls hard to 7500 rpm or beyond. This extends your usable powerband, allowing you to hold gears longer on track or during highway pulls. The Evo’s tall gear ratios benefit from this extended RPM range.

Better Throttle Response

The AMS 20G’s lighter rotating assembly (billet wheels vs. cast) reduces inertia, improving transient response. When you lift off and then get back on the throttle, the turbo recovers boost pressure faster than a heavier, larger turbo. This makes the car feel more lively and connected.

Sound and Driving Character

With the larger compressor and turbine, the AMS 20G produces a deeper, more aggressive spool sound. The wastegate dump (if plumbed) adds a distinctive note. Many owners report that the upgrade makes the Evo feel like a real race car without sacrificing streetability.

Supporting Modifications: What Else Do You Need?

A turbo upgrade is rarely a standalone swap. To safely and effectively run the AMS 20G, consider the following list of modifications. Think of them as prerequisites for reaching the 380+ whp region.

  • Fuel System: Walbro 255 (or 450) high-flow fuel pump + 850–1050 cc injectors. The stock fuel pressure regulator may also need upgrading at higher flow rates.
  • Engine Management: ECUFlash (with a proper tune) or a standalone like AEM EMS, Haltech, or Link. Tuning is mandatory—the stock maps will not be safe.
  • Exhaust: 3-inch turbo-back exhaust (downpipe + test pipe/midpipe + cat-back). A free-flowing exhaust reduces backpressure and lets the turbo spool faster.
  • Intake: 4-inch or 3.5-inch intake pipe with a high-flow air filter (e.g., K&N, AEM, HKS). The stock airbox is restrictive at higher flow.
  • Intercooler: Aftermarket front-mount intercooler (FMIC) with 3-inch piping. This is critical for maintaining power on warm days and during extended pulls.
  • Boost Control: A quality boost controller (manual or electronic) is necessary to set and maintain the desired boost level. A 3-port solenoid (e.g., MAC valve) is often used with ECU control.
  • Crankcase Ventilation: A catch can setup is recommended to prevent oil from entering the intake tract, which can cause detonation.
  • Clutch: The stock clutch may slip above 380 whp. Consider an upgraded clutch and lightweight flywheel if you plan to make 400+ whp.
Important: Never install the AMS 20G without the necessary fuel and tuning upgrades. Running the turbo on the stock injectors and fuel pump is extremely dangerous and can destroy your engine in a single pull.

Installation Considerations: What’s Involved?

The AMS 20G is designed as a direct bolt-on replacement for the stock turbo on Evo VIII and IX (and some Evo X applications with an adapter kit). However, the installation process still requires mechanical competence. Here’s a high-level overview of the steps.

Step 1: Remove the Stock Turbo

Drain the oil and coolant. Disconnect the intercooler piping, intake pipe, and exhaust downpipe. Unbolt the wastegate actuator and oil/coolant lines. The stock turbo comes off with the manifold still attached in many cases. Be careful not to damage the oil return line.

Step 2: Prepare the Manifold

The AMS 20G often requires porting the exhaust manifold to match the larger turbine inlet gasket. Use a template or measure carefully. Failure to port can cause a gasket mismatch and exhaust leaks. Some kits include a new manifold or adapter.

Step 3: Install the AMS 20G

Fit the turbo to the manifold with a new gasket. Attach the oil feed and return lines (use AN fittings for reliability). Reconnect the coolant lines (if water-cooled). Attach the downpipe and intercooler piping. The AMS 20G usually includes a new dump pipe or requires welding a flange onto the stock O2 housing.

Step 4: Tune the Car

After installation, start the engine and check for leaks. Then drive carefully to the tuner. Do not boost hard until the tune is complete. A wideband O2 sensor and boost gauge are strongly recommended during the break-in period.

While many DIY enthusiasts can handle the AMS 20G swap, it’s wise to have a professional shop do the installation, especially if you’re unfamiliar with Evo turbo systems. A mistake—like an oil leak or improper torque on the manifold studs—can lead to fire, oil starvation, or exhaust leaks. Count on 8–12 hours of labor for a first-time install.

Real-World Performance: Dyno Results and Owner Feedback

Community data confirms the AMS 20G’s reputation. On the EvoM forum and other enthusiast sites, owners with a “stage 2” setup (fuel pump + injectors + FMIC + 3-inch exhaust + tune) commonly report dyno numbers between 390 and 420 whp on 93 octane at 25–26 psi. On E85, those numbers climb to 430–460 whp. For example, one well-documented build: a 2006 Evo IX with full bolt-ons and the AMS 20G made 410 whp and 380 lb-ft on a Mustang dyno (which reads slightly lower than Dynojet). On the street, owners note that the turbo “wakes up” around 3500 rpm and pulls hard to the 7500 rpm redline. Many describe it as the perfect turbo for a daily driver that also sees weekend track duty.

Reliability is generally excellent when the setup is properly tuned and maintained. Common issues are limited to cracked manifolds if the turbo is overboosted, or oil line leaks if old rubber lines are reused. Using braided stainless steel lines solves the latter. The AMS 20G itself is built to last; its billet wheel is stronger than cast wheels and resists fatigue.

For additional reading and owner experiences, check the AMS Performance product page and EvoM Forum. Another useful resource is the AMS Performance official website for current specifications and kit options. For dyno charts and community discussions, EvolutionM.net has an extensive thread on the AMS 20G turbo.

Conclusion: Is the AMS 20G Turbo Worth It?

The AMS 20G turbo delivers a substantial power increase—roughly 120–170 additional wheel horsepower over stock—without sacrificing the responsive, daily-drivable character that makes the Evo special. When paired with proper supporting modifications and a high-quality tune, it pushes the Evo into a performance bracket that can hang with modern sports cars while retaining classic rally-car charm. Spool is quick, top-end is strong, and the build quality is proven. For Evo owners who want more than the stock 16G offers but aren’t ready to commit to a larger, laggier turbo, the AMS 20G is an excellent choice.

Before purchasing, consider your budget for supporting mods and tuning. The turbo itself is a start, but the full system needs to be balanced. If you’re prepared to invest in fuel, intake, exhaust, and intercooler upgrades, the AMS 20G will reward you with a truly exhilarating driving experience. It’s an upgrade that turns a fast car into a seriously quick one.

For further details on installation or tuning, consult a professional shop like EVOMS (AMS Performance), or dive into the community knowledge on EvoM’s engine and turbo section. A well-built AMS 20G Evo is a driver’s dream—powerful, responsive, and incredibly engaging.