The 4B11T engine found in Mitsubishi's Lancer Evolution X, as well as the Lancer Ralliart and some other models, is a turbocharged 2.0-liter inline-four that has earned a reputation for robustness and tuning potential. While stock output sits at around 291 horsepower (Evolution X) or 237 horsepower (Ralliart), the engine’s cast-iron block, forged crankshaft, and aluminum DOHC cylinder head with MIVEC variable valve timing provide a solid foundation for serious power gains. With the right combination of modifications, the 4B11T can reliably surpass the 300-horsepower mark and go much further. In this guide, we break down the essential upgrades — from turbochargers to exhaust systems and beyond — that will help you achieve 300+ wheel horsepower while maintaining drivability and durability.

Understanding the 4B11T Engine

The 4B11T is a member of Mitsubishi’s “4B1” family, sharing architecture with naturally aspirated versions but featuring a twin-scroll MHI TD04HL-15T turbocharger (Evolution X) or a smaller TD03 turbo (Ralliart). The engine uses a semi-closed deck design with cast-iron cylinder liners, making it capable of handling 400–500 horsepower on the stock bottom end with proper tuning. The cylinder head features 4-valve per cylinder with sodium-filled exhaust valves on later models, and the MIVEC system adjusts both intake and exhaust cam timing. However, reaching the 300+ horsepower target requires upgrading key systems to support increased airflow, fuel delivery, and thermal management.

Turbocharger Upgrades

The turbocharger is the heart of any forced-induction power increase. The stock Evo X turbo (TD05HR-15T) is capable of around 330–350 crank horsepower with light modifications, but it quickly runs out of steam beyond that. For a reliable 300+ whp (which translates to roughly 360–380 crank horsepower), you need a turbo that can deliver more mass flow without excessive backpressure.

Stock Turbo Limitations

The stock twin-scroll turbo spools quickly and provides excellent low-end torque, but its compressor and turbine wheels are size-restricted. At boost levels above 23–24 psi, the turbo becomes inefficient, generating excessive heat and high drive pressures. This leads to knock and limits power output. For 300+ whp, the stock unit will be near its maximum safe limit — and small variations in temperature or fuel quality can cause problems.

Top Turbo Options for 300+ HP

Several aftermarket turbo choices allow you to eclipse 300 whp without sacrificing too much response. The following are proven performers on the 4B11T:

Garrett GTX2860R

The Garrett GTX2860R is a popular upgrade for those seeking quick spool and solid mid-range power. Its 56mm compressor wheel with extended-tip technology flows up to 45 lb/min, enough for 400+ horsepower. With a suitable tune, this turbo can deliver 320–350 whp on pump gas, with spool only slightly behind the stock unit. It requires a new turbo manifold and downpipe adapter.

BorgWarner EFR Series (EFR 6758 or EFR 7064)

BorgWarner’s EFR series offers integrally cast turbine housings with stainless steel bumps, dual ball bearings, and integrated wastegates on some models. The EFR 6758 (58mm compressor) is excellent for 300–350 whp, while the EFR 7064 can push past 400 whp. These turbos are known for excellent response and high efficiency. They require careful selection of the turbine housing A/R for your power goals.

MHI TD05 18G / 20G Conversions

For budget-minded builders, upgrading the stock MHI turbo to an 18G or 20G compressor wheel is a cost-effective path. These upgrades use the stock turbine housing and modified compressor cover, maintaining twin-scroll advantages. An 18G can produce 330–350 whp, while a 20G can reach 370–400 whp, though spool is slightly delayed. Be aware that these upgrades push the stock turbine wheel close to its limit, so monitoring exhaust backpressure is critical.

Supporting Mods for Turbo Upgrades

Any turbo upgrade beyond the stock unit requires a new exhaust manifold (or ported stock manifold with adapter), a boost control solenoid (or upgraded electronic boost controller), and matching downpipe. For twin-scroll turbos, ensure the manifold retains twin-scroll separation. Also consider a ported or upgraded wastegate to prevent boost creep. A quality intake to reduce inlet restriction is mandatory.

High-Performance Intercooler

Lowering intake air temperature is essential when increasing boost. The stock front-mount intercooler (FMIC) on the Evolution X is decent but becomes a bottleneck above 350 whp. Aftermarket intercoolers with a larger core volume and better fin density reduce pressure drop and heat soak. For a 300+ whp build, look for an intercooler that is at least 50% thicker than stock, with cast end tanks for even airflow distribution. Brands like PRL, AMS, or ETS offer direct-fit units that support 500+ horsepower. Pair the intercooler with an upgraded silicone hose kit to eliminate boost leaks at the charge pipe connections.

Exhaust System Upgrade

Restrictive exhaust components create backpressure that limits power and spool. The stock Evolution X downpipe includes a restrictive catalytic converter. Upgrading to a full turbo-back exhaust system is one of the best mods for freeing horsepower.

Recommended exhaust configuration for 300+ whp:

  • Downpipe: Replace with a 3-inch downpipe (catless or high-flow catalytic option). A divorced or dual-pipe wastegate design helps maintain boost control.
  • Mid-Pipe/Test Pipe: Use a 3-inch test pipe to eliminate restrictive secondary cat (if your local regulations allow).
  • Cat-Back Exhaust: 3-inch mandrel-bent tubing with a straight-through muffler reduces backpressure while allowing a refined sound. Many owners choose a dual-exit style that mimics the Evo X's layout.

A full 3-inch turbo-back exhaust can gain 15–25 whp over stock on a tuned 4B11T. Avoid diameters larger than 3 inches until you exceed 500 whp, as 3.5 or 4-inch systems can hurt torque and increase drone noise.

ECU Tuning

Tuning is the single most important step for making power and keeping the engine alive. Without proper calibration, upgraded hardware is useless — and dangerous. The 4B11T engine uses an ECU that can be tuned via OpenECU (EcuFlash) or professional platforms like ECUTek. Both offer access to fuel maps, ignition timing, boost control, and advanced knock detection.

Flash Tuning vs. Standalone

For a 300+ whp build, flash tuning via ECUTek or OpenECU is cost-effective and retains all factory features (cruise control, AC, cold start). ECUTek provides excellent knock control with adaptive timing, and it is widely supported by professional tuners. Standalone ECUs like Motec or Haltech are overkill for this power level unless you plan to significantly exceed 400 whp later.

Boost Control and Knock Management

Your turbo upgrade will require revising the boost target table. Use an electronic boost controller (e.g., MAC valve for closed-loop control) to maintain stable boost across the rpm range. Tune for peak boost around 22–26 psi depending on fuel octane (93 octane for 300–330 whp, less for lower octane). Ignition timing must be conservative on pump gas — aim for 10–12 degrees of advance at peak torque, ramping up to 18–22 degrees at redline. Reliable knock detection through an aftermarket knock sensor (or using ECUTek's knock control) is crucial.

Fuel System Upgrades

Stock fuel injectors (560cc/min on Evo X, smaller on Ralliart) max out around 350 crank HP. For 300+ whp, you need to upgrade the fuel system to maintain proper air-fuel ratios (AFRs) under high boost.

Injectors and Pump

  • Injectors: Upgrade to 1000–1200cc/min high-impedance injectors (e.g., Injector Dynamics, Fuel Injector Clinic) that provide headroom for future upgrades.
  • Fuel Pump: Install a Walbro 450 (or DW400) in-tank fuel pump with a direct wiring harness to maintain voltage. The stock pump drops pressure above 350 whp.

Fuel Lines and Pressure Regulator

At 300+ whp, stock feed lines are sufficient, but upgrading to a stainless braided line and a fuel rail is recommended for consistency. An adjustable fuel pressure regulator set at 43 psi (with vacuum reference) helps maintain stable pressure. Always run a return-style system if using a FPR — plug the stock return line from the pump hanger.

Additional Supporting Mods

Beyond the core upgrades, several smaller modifications ensure the engine lives a long life at higher power levels.

Intake and Blow-Off Valve

A cold air intake with a dry-flow filter reduces restriction and protects the turbo from debris. The stock plastic intake pipe can collapse under high vacuum — replace it with a silicone or aluminum pipe. A vent-to-atmosphere blow-off valve is not necessary for 300 whp; the stock recirculating valve works well. If upgrading, choose a quality unit like the HKS SSQV or TiAL Q to avoid boost leaks.

Oil Cooling and Drivetrain

At power levels above stock, oil temperatures rise. Install an oil cooler kit (e.g., Setrab or Mishimoto) with a thermostat. For the drivetrain, the Mitsubishi SST dual-clutch transmission can handle 350–400 whp if properly maintained, but it is wise to upgrade to a stronger clutch pack and a daily-driver-friendly tune. For manual cars, upgrade the clutch to a competition twin-disk (e.g., ACT, Exedy) to handle the torque.

Reliability Considerations

Pushing a 4B11T to 300+ whp requires attention to cooling, lubrication, and maintenance. Use high-quality synthetic 5W-30 or 5W-40 oil (e.g., Motul 300V or Red Line). Change oil and filter every 3,000 miles. Monitor coolant temperatures — consider an upgraded radiator and a high-flow water pump if you track the car. Always allow the engine to warm up before hard driving and cool down after a run. EGT and wideband O2 sensors are essential for tuning and ongoing monitoring.

Conclusion

Achieving over 300 horsepower on the 4B11T is an attainable goal with a systematic approach. Start with a turbo upgrade that matches your power target, pair it with a high-performance intercooler and a 3-inch exhaust, and dial in the tune with a reputable ECU flash. Don't neglect the fuel system — proper injectors and a pump are non-negotiable. Supporting mods like an oil cooler, intake, and drivetrain upgrades will keep the car reliable for street or track use. For those seeking detailed build guides and tuner recommendations, consult resources like the EvolutionM forums, MAPerformance for parts, and ECUTek for tuning solutions. With careful planning and execution, your 4B11T will deliver a thrilling and dependable 300+ horsepower driving experience.