Upgrading your Mitsubishi Evolution’s turbocharger is one of the most effective ways to unlock substantial horsepower gains and sharpen throttle response. The BorgWarner EFR 8374 turbocharger, with its advanced dual ball bearing cartridge, titanium-aluminide turbine wheel, and integrated recirculation valve, offers a proven upgrade for Evo owners targeting between 500 and 700 wheel horsepower. This guide walks through the complete installation process—from workspace preparation and old turbo removal to final tuning considerations—so you can perform the swap confidently and correctly.

While the process is straightforward for experienced DIYers, every step demands attention to detail. Flawless oil supply routing, proper wastegate setup, and secure coolant line connections are non-negotiable for long turbo life. Follow the sequence below and refer to factory service manual torque specifications where noted. Let’s get started.

Tools and Materials Needed

Gathering the right equipment before lifting the hood saves hours of frustration. The BorgWarner EFR 8374 installation requires specialty tools alongside standard shop items. Here’s the complete list:

  • Socket set (metric, 8–19 mm) – Deep sockets help reach tight fasteners near the manifold.
  • Wrench set (combination and flare-nut wrenches) – Flare-nut wrenches prevent rounding oil and coolant line fittings.
  • Torque wrench (3/8” and 1/2” drive) – Critical for turbo-to-manifold bolts and oil drain flange.
  • Turbocharger installation kit – Often includes new studs, lock washers, copper nuts, and gaskets specifically for the EFR 8374.
  • New gaskets – Manifold-to-head, turbo-to-manifold, drain flange gasket. Use OEM quality or multi-layer steel.
  • Oil and coolant lines – The EFR 8374 uses -4 AN oil feed and -10 AN oil drain. Coolant lines should be stainless braided Teflon.
  • Intercooler piping and silicone couplers – Often need adjustment because the EFR 8374 compressor outlet position differs from the stock turbo.
  • Vacuum line kit – For boost reference to the internal wastegate actuator.
  • Safety glasses, nitrile gloves, and a fire extinguisher – Basic safety gear for any fuel-adjacent work.

Optional but highly recommended: a borescope for inspecting the turbo oil drain port and a 4-post lift or sturdy jack stands for better under-car access.

Preparation Steps

Workspace and Vehicle Setup

Park the Evo on a level concrete surface. Engage the parking brake and place wheel chocks behind the rear tires. Disconnect the battery negative terminal and wait five minutes for the ECU capacitors to discharge. This prevents accidental fuel pump activation or spark when manipulating wiring near the turbo.

Draining Fluids

Drain the engine oil and coolant completely. The oil drain plug is on the oil pan, and the coolant drains via the petcock on the radiator and the block drain bolt (driver’s side near the thermostat housing). Collect old fluids in approved containers. Removing fluids reduces spill risk when disconnecting turbo lines and prevents debris from entering the oil gallery during the swap.

Access Preparation

Remove the engine beauty cover, the intercooler piping, and the air box assembly. On most Evo models, removing the radiator fan shroud and the alternator will greatly improve access to the turbo lower bolts. Label every vacuum line and connector with masking tape before disconnecting. Photograph the stock vacuum routing—this reference is invaluable when connecting the EFR 8374’s recirculation valve and wastegate lines.

Removing the Old Turbocharger

Removal is the reverse of installation, but careful technique prevents damage to manifold studs and surrounding components.

Step 1: Disconnect Lines and Sensors

Unplug the oxygen sensor and any boost control solenoid connectors. Use a flare-nut wrench to disconnect the oil feed line at the turbo and the block. Coolant lines can be cut if they are crimp-style; otherwise, unbolt them at the turbo and the pipe connection. Cap all open fittings with rubber vacuum caps to keep dirt out.

Step 2: Remove Intake and Exhaust Piping

Loosen the clamps on the intake tube between the air filter and turbo compressor inlet. Remove the downpipe bolts (four at the turbo, two at the catalytic converter flange). Support the downpipe with a jack stand to avoid stressing the flex section. Disconnect the intercooler pipes at the compressor outlet and throttle body. Label each pipe section if they are not stock.

Step 3: Unbolt Turbo from Manifold

Start by removing the five copper nuts holding the turbo to the exhaust manifold. Apply penetrating oil the night before—copper nuts on heat-cycled studs are notoriously stubborn. Work from the bottom up. With all nuts removed, gently rock the turbo back and forth to break the gasket bond. Lift the turbo straight up and out. Inspect the manifold face for flatness; a warped manifold will cause exhaust leaks with the new EFR.

Step 4: Clean and Inspect

Scrape old gasket material from the manifold using a plastic scraper. Inspect the studs: replace any that are stretched or cross-threaded. Check the oil drain port in the block for sludge—use a pick or small brush to clean it. A clogged drain is the #1 cause of EFR turbo seal failure.

Installing the BorgWarner EFR 8374 Turbo

The EFR 8374 shipped from BorgWarner includes the turbine housing clocked in a standard position. You may need to rotate the center housing or turbine housing for optimal line routing. Loosen the V-band clamp carefully, align the actuator bracket with the compressor cover orientation, then retighten to 5 Nm.

Step 1: Mount the Turbo to the Manifold

Place a new gasket on the manifold. Lower the EFR 8374 into position, aligning the oil drain flange with the block port. Use the supplied copper nuts and washers; hand-tighten first, then torque in a cross pattern to 30 Nm (consult BorgWarner specs—some housings require 25 Nm). Do not over-torque—the cast iron manifold is strong, but the studs can gall.

Step 2: Connect Oil and Coolant Lines

  • Oil feed: Use a -4 AN stainless line with a restrictor (0.040” or 1.0 mm orifice) in the block fitting. Teflon tape on NPT fittings only; avoid tape on AN unions. Tighten to 14 Nm.
  • Oil drain: The -10 AN drain line must slope downward continuously with no dips or kinks. Use a 45° or 90° fitting at the turbo to maintain gravity drain. Torque the drain flange bolts to 10 Nm.
  • Coolant lines: Connect the inlet (from the water pipe) and outlet (to the thermostat housing or coolant reservoir). Purge air by leaving one end loose until coolant flows, then tighten.

Step 3: Attach Intake and Exhaust Piping

Bolt the downpipe to the turbine outlet using a new gasket. Use anti-seize on the studs. For the intake side, install the compressor outlet pipe with a silicone coupler and T-bolt clamp. The EFR 8374’s 4” compressor inlet may require a larger intake tube—plan ahead with a 4” to 3.5” reducer. Connect the recirculation valve (the turbo’s built-in BOV) to the intake pipe using the supplied hose.

Step 4: Wastegate and Boost Control

The EFR 8374 features an internal wastegate with a 1.0 bar (14.5 psi) spring by default. Connect the actuator canister to the compressor cover boost reference port using 4 mm silicone hose. If using an external boost controller, tee into this line. A boost controller is recommended for safe tuning—start with low boost and increase only after professional calibration.

Final Steps and System Check

Reassembly and Fluid Fill

Reinstall the alternator, fan shroud, intercooler piping, and air box. Refill the engine with 5W-40 oil (Mobil 1 or Motul) and coolant (50/50 ethylene glycol distilled water). Pour oil into the turbo oil feed port (disconnect feed line at the turbo, pour ~200 ml into the port) to pre-lubricate the bearings—this prevents dry start damage.

Leak Testing and Purge

Start the engine and let it idle for 30 seconds. Watch for oil leaks at the drain flange, feed fitting, and coolant weep holes. If the turbo smokes, it may be oil residue from the bearing cavity—this usually clears after a minute. Increase RPM to 2000 and hold for two minutes to circulate coolant and purge air. Check all clamps and hoses for secure fit.

Test Drive and Break-in

Take the Evo for a gentle 15-minute drive keeping boost below 10 psi. This seats the ring seals and verifies proper operation. Return to the shop, re-torque downpipe bolts, and check all fluid levels. After the first 50 miles, perform a full boost pull on a private road to confirm wastegate function and boost curve.

Post-Installation Tuning and Optimization

Installing a larger turbocharger without recalibrating the ECU is dangerous. The EFR 8374 flows significantly more air than stock, leaning out air-fuel ratios and spiking boost. Professional tuning via EcuFlash, Cobb Accessport, or standalone ECU (MoTeC, Syvecs) is mandatory.

Fuel System Upgrades

Expect to need larger injectors (at least 1000 cc/min), a high-pressure in-tank fuel pump (AEM 340 or Walbro 525), and possibly a fuel pressure regulator. The EFR 8374 at 30+ psi can demand over 600 lph fuel flow.

Boost Control and Safety

Use a boost controller with a map switch for low/high boost. Set the low boost map (e.g., 20 psi) for daily driving and a high map (28-32 psi) for track use. Always log AFR (target 11.5-12.0:1 at WOT) and knock count. Consider an oil catch can to reduce crankcase pressure that can push oil past turbo seals.

Important: Never run the EFR 8374 without an oil restrictor in the feed line. The twin ball bearing cartridge requires only 40–60 psi oil pressure at idle; higher pressure forces oil past the seals. Always use a -4 AN feed line with a 0.040” restrictor.

Common Pitfalls and How to Avoid Them

  • Oil drain slope – The drain must be vertical or at least 45° downward with no low points. A 90° fitting immediately after the turbo is acceptable but use a long-radius tube.
  • Inlet clogging – Dirt ingestion destroys compressor wheels. Use a quality air filter (AEM Dryflow) and a clean intake pipe with no leaks downstream.
  • Exhaust backpressure – Factory downpipe may choke the EFR 8374. Upgrade to a 3” or 3.5” downpipe with a high-flow catalytic converter.
  • Heat management – Wrap the downpipe in DEI titanium wrap and install a turbo blanket to keep underhood temperatures below 200°F. Aftermarket heat shields are available from Full Race or PTP.
  • Recirculation valve orientation – The integrated BOV must be connected to the compressor inlet, not vented to atmosphere, to maintain safe air metering.

Conclusion

The BorgWarner EFR 8374 turbocharger transforms the Mitsubishi Evolution from a quick street car into a serious mid-600 whp contender. With careful installation—proper drain routing, oil restrictor, and V-band clocking—you’ll enjoy immediate throttle response and sustained high-rpm power. Remember that a turbo upgrade is a system change: budget for tuning, larger injectors, and fuel system improvements. If any step feels unclear, consult a professional shop like English Racing or AMS Performance.

For further reading, refer to the official BorgWarner EFR technical manual and the EvolutionM turbo installation stickies. A quality video walkthrough can also supplement this guide. Drive safely and enjoy the spool.