Upgrading Your Wrx’s Turbocharger to a Mitsubishi Td05-20g: Power Gains and Tuning Tips

Upgrading your Subaru WRX's turbocharger is one of the most effective ways to unlock serious horsepower and transform the car's character. Stock turbos like the TD04 or VF48 offer decent low-end spool, but they run out of steam quickly when pushing for big numbers. The Mitsubishi TD05-20G has long been a favorite among Subaru enthusiasts looking for a hard-hitting, reliable upgrade that balances power with drivability. Originally found on Mitsubishi Evos and later adopted by the aftermarket, this turbocharger brings genuine big-turbo performance without requiring a full rotated mount setup. In this article, you'll learn exactly what the TD05-20G delivers in terms of power, what modifications you need to support it, and the tuning tips required to make it all come together safely.

Understanding the Mitsubishi TD05-20G Turbocharger

The Mitsubishi TD05-20G is a turbocharger that belongs to the Mitsubishi Heavy Industries (MHI) TD05 family. The "20G" designation refers to the compressor wheel size—a 20G inducer that flows significantly more air than the stock WRX turbo. While the TD05 housing itself is similar to earlier 16G and 18G variants, the 20G uses a larger, more aggressive compressor wheel that pushes the air flow ceiling much higher. This gives you a turbo that can comfortably support 350–400 whp on pump gas when paired with the right supporting mods.

Key features of the TD05-20G in a WRX application include:

High flow capacity: The 20G compressor is capable of flowing around 47–50 lb/min, enough to support over 400 horsepower at the crank.
Durable journal bearing core: MHI's twin-entry journal bearing design is known for long service life when oil quality and cooling are maintained.
Improved spool: Although larger than stock, a properly matched TD05-20G can still reach full boost by 3500–3800 rpm on a 2.0L or 2.5L WRX engine, making it far more responsive than larger rotated turbos.
Direct bolt-on compatibility: Many aftermarket TD05H/20G units are offered with a Subaru flange (T3/T04E or stock location twin-scroll) allowing a relatively straightforward installation without custom fabrication.

It's important to note that the TD05-20G is often sourced as a new aftermarket unit from manufacturers like Blouch, FP, or Speed of Air, rather than a junkyard pull. These units may incorporate upgraded thrust bearings, billet compressor wheels, and ported housings for better efficiency and reliability on Subaru boxer engines.

Power Gains and Performance Expectations

The power gains from bolting on a TD05-20G depend heavily on your engine platform, boost level, and supporting mods. On a WRX with a stock EJ205 (2.0L) at 18–20 psi, you can expect somewhere in the range of 300–330 whp, which is a significant jump from the stock TD04's 180–210 whp. On a 2.5L WRX (EJ255/EJ257), the extra displacement allows the 20G to spool even faster, and with proper tuning and fuel system upgrades (including a larger fuel pump and injectors), 350–390 whp is achievable on 91–93 octane pump gas. Ethanol blends like E85 can push you past 420 whp with headroom to spare.

Dyno comparisons commonly show:

Stock TD04 (EJ205): 190 whp / 200 wtq (peak torque by 2800 rpm, falls off hard after 5000 rpm)
TD05-20G (EJ205, 20 psi): 310 whp / 300 wtq (starts building boost by 3000 rpm, holds strong to redline)
VF48/52 (EJ257, 18 psi): 290 whp / 310 wtq (good midrange, runs out of steam at higher rpm)
TD05-20G (EJ257, 22 psi): 380 whp / 360 wtq (linear power curve, excellent top-end pull)

Real-world spool characteristics: on a 2.5L engine, boost threshold sits around 3000–3200 rpm, with full boost by 3700 rpm. On a 2.0L, you may see full boost around 3800–4000 rpm, which is still very tractable for a street-driven car. The 20G's larger housing gives you the ability to make power well past 7000 rpm, making it a solid choice for autocross, time attack, and track days where top-end extends beyond the stock turbo's ceiling.

Essential Supporting Modifications

No turbo upgrade works in isolation. To safely run a TD05-20G and avoid leaning out, knocking, or frying the engine, you must upgrade several supporting systems:

Fuel System

Fuel pump: A Walbro 255 lph (or AEM 340 lph) is mandatory to maintain fuel pressure under high boost. Stock pumps tend to drop off at 300+ whp.
Fuel injectors: Target 750–850 cc/min injectors on pump gas, and 1000 cc/min or larger if planning ethanol. Stock top-feed injectors will max out very quickly.
Fuel pressure regulator: An adjustable FPR can help maintain consistent pressure, especially if you have a modified return line.

Intake & Induction

Cold air intake or short ram: A larger diameter CAI (usually 3″) reduces restriction. Avoid oiled filters that can contaminate the MAF sensor.
Turbo inlet hose: The stock plastic inlet collapses easily under higher boost. Upgrade to a silicone or aluminum inlet that matches the 20G's compressor inlet size (typically 2.4″–2.75″).
Intercooler: A larger front-mount intercooler (FMIC) or a high-capacity top-mount (TMIC) is essential to keep intake air temperatures down. The stock intercooler will heat-soak rapidly, causing detonation and power loss.

Exhaust System

Downpipe: A 3″ catless downpipe matched to the turbo's turbine outlet (often a 7cm or 8cm housing) is non-negotiable. A restrictive downpipe chokes the 20G's flow and spools the turbo slower.
Full exhaust: A 3″ cat-back (or at least a high-flow muffler) reduces backpressure. Larger exhausts also improve steady-state power on the dyno.

Engine Management & Tuning

A factory ECU cannot properly control fueling and ignition timing at the airflow levels of a 20G. You need a flash tune or standalone engine management. The most common solutions include:

Cobb Accessport with a pro-tune from a reputable tuner (either remote or on a dyno).
Open-source tuning using RomRaider or EcuFlash, if you have experience and a wideband O2 sensor.
Standalone ECUs like Haltech or MoTeC for maximum control, though overkill for most street builds.

Regardless of the platform, a wideband oxygen sensor must be used to monitor air-fuel ratios. Target AFRs: 11.5–11.8:1 under full boost for pump gas; 11.8–12.2:1 for ethanol blends (depending on ethanol content and timing).

Supporting Cooling

Oil cooler: A setrab or Mocal sandwich-plate cooler helps keep oil temperature below 220°F during sustained pulls. Heat is the biggest enemy of journal bearing turbos.
Upgraded radiator: A Koyo or CSF aluminum radiator with a higher capacity core keeps coolant temps in check when the 20G dumps heat into the system.
PCV and catch can systems: Reducing crankcase pressure prevents oil from being pushed out through seals and helps the turbo's journal bearings survive.

Installation Considerations

Installing a TD05-20G on a WRX is a weekend-job for a competent DIYer, but there are several pitfalls to avoid:

Oil feed and drain: The stock WRX turbo uses a banjo bolt oil feed; the TD05-20G often requires an -3AN or -4AN feed line and a -10AN drain line. Ensure proper restrictor size to prevent over-oiling.
Coolant lines: Some aftermarket 20G units are water-cooled; you'll need to adapt the stock coolant hoses or run separate lines to a sandard reservoir.
Wastegate setup: Many TD05-20G units come with an internal wastegate (flapper style) that must be correctly adjusted to hold boost. Check the wastegate port size—if it's too small, boost creep can occur. An external wastegate is sometimes retrofitted for better control.
Gaskets and fasteners: Always replace turbo-to-header gaskets and downpipe gaskets with OEM or equivalent. M10 studs / nuts should be torqued to spec and rechecked after a heat cycle.
Fitment clearance: On some years (particularly 2002–2005), the TD05-20G may contact the engine block or ABS pump. A 5mm spacer or hammer massage may be required. Always mock-fit the turbo before final assembly.

Tuning Tips for the TD05-20G

Getting the most out of your 20G requires careful calibration. Here are specific tuning tips for this turbo:

Boost Control

Use a 3-port boost control solenoid (e.g., GM BCS, Cobb EBCS). Do not rely on a manual boost controller—response is too crude and you risk over-boost damage.
Set a conservative base boost of 16–18 psi for the first few pulls to verify fueling and knock correction. Gradually ramp up to 20–23 psi on pump gas (depending on fuel quality and octane).
Watch for boost creep: if boost overshoots target by 3+ psi at high rpm, you may need a larger wastegate port or an external gate.

Ignition Timing

On pump gas (91–93 octane), target a timing curve that peaks around 16–18° BTDC at full boost. Too much timing early can cause knock on a 20G due to its denser air charge.
Use knock detection (stock sensor or stand-alone) and pull timing aggressively if you see knock counts above 3–4. A 20G can be knock-prone if the tune is too aggressive.
Consider a conservative tune on pump gas; the 20G will still make plenty of power without pushing the edge.

Fuel Trimming

MAF scaling is critical: the 20G flows more air than stock, so the MAF table must be rescaled. A poorly scaled MAF causes lean spots and stumbling.
Use speed-density or proper MAF scaling for your intake setup. A blow-through MAF arrangement can reduce turbulence errors.
Target an AFR of 11.5–11.8 at WOT for safety; richer than that wastes power, leaner invites knock.

Dyno Tuning

While a remote e-tune can get you close, a dyno tune is strongly recommended for a 20G upgrade. The dyno gives real-time torque, power, and air-fuel data that a street pull cannot replicate. A good tuner will also verify that the turbo is spooling correctly and that the wastegate is holding boost.

Common Issues and Troubleshooting

No upgrade is without challenges. Here are the most common problems with the TD05-20G on a WRX and how to address them:

Boost leak	Check all intercooler couplers, intake pipe connections, and compressor outlet for leaks. Use a boost leak tester (buy one from a tuning shop) at 20 psi. A small leak can cause power loss and spiking.
Overheating	Ensure your coolant system is in good health: change the thermostat, bleed the system, and consider a larger radiator. Also check that the oil cooler is effective.
Engine knock / detonation	This is usually a tuning issue. Check that you're not running too lean, that timing is not too aggressive, and that your fuel octane is adequate. Also verify that the MAF is not reporting falsely low airflow.
Wastegate creep	If boost continues to rise past redline, you may need a larger wastegate port or a different flapper. Some tuners address this by using a boost controller that bleeds air to keep the gate open earlier.
Compressor surge	Typically occurs at part-throttle or under high load at low rpm. Sound like a fluttering or chirping. Solutions include a BOV that's properly adjusted, or a recirculation setup. The 20G's surge line is usually above the operating range on a 2.5L, but can occur on 2.0L with too-aggressive boost maps.
Oil leaks from turbo seals	Often caused by draining issues: the return line must be larger than the feed line and must slope downward without kinks. Also check crankcase pressure—excessive blow-by forces oil past the seals.

Regular maintenance intervals—oil changes every 3,000 miles with a high-quality synthetic, coolant flushes every two years, and boost leak checks annually—will keep your 20G running strong for many miles.

Cost Analysis and Value

Is the TD05-20G worth the investment compared to other options? Let's break down typical costs:

New aftermarket TD05-20G turbo (Blouch, FP, etc.): $1,200–$1,800
Supporting mods (fuel system, intercooler, inlet, downpipe, tuning): $1,500–$2,500
Professional dyno tune: $400–$700
Total estimated cost: $3,100–$5,000

This contrasts with a rotated turbo setup (like a GT30/35) which can cost $3,000–$5,000 just for the turbo kit, plus more for custom fabrication. The TD05-20G offers a much lower barrier to entry while still providing genuine 350–400 whp capability. For comparison, a stock location VF-52 upgrade on a 2.5L WRX costs about $1,200 (turbo) and yields 290–310 whp—good, but leaves power on the table. The 20G provides 20–30% more top-end power for a similar overall investment.

When you factor in resale value (these turbos are popular and easily sold), the cost per horsepower is excellent. For a street-driven WRX that sees occasional track or autocross duty, the TD05-20G remains one of the best value high-power upgrades you can do.

Final Considerations and Future-Proofing

Before you purchase a TD05-20G, think about your power goals and how you use the car. If you intend to upgrade further later (e.g., built block or a larger turbo), choose a turbo that can grow with you. However, for 350–400 whp on pump gas or 420+ whp on ethanol, the 20G is a sweet spot. It is also compatible with built engines up to about 8,000 rpm if you keep boost moderate.

Consider upgrading to a billet compressor wheel version—these offer slightly faster spool and better efficiency than traditional cast wheels. Brands like Blouch Turbo offer a billet 20G that has proven reliable on many Subarus. Also, look at IAG Performance for complete upgrade kits that include oil lines, gaskets, and inlet hoses all matched to the 20G. For tuning support, Cobb Tuning is a trusted resource for Accessport base maps and pro-tune referrals.

Finally, never skip a professional inspection of your current engine health. Compression and leakdown tests should be done before any turbo upgrade. A tired engine with 150,000+ miles may not hold together under 350 whp. Budget for a rebuild if needed—the TD05-20G will quickly expose any weak link in your bottom end.

In summary, upgrading your WRX with a Mitsubishi TD05-20G turbocharger is a proven path to serious power gains that transform the car's acceleration and top-end charge. With the right supporting modifications—fuel system, intercooler, exhaust, inlet, and a proper tune—you can build a reliable, hard-hitting street machine that punches well above its weight class. Approach the upgrade with careful planning, accept that tuning is not optional, and you'll be rewarded with a turbo setup that delivers thrills every time you step on the gas.