The A45 turbo upgrade with the MHI TD04HL-19T turbocharger represents one of the most cost-effective and reliable paths to significantly increasing horsepower on Mercedes-AMG A45 and CLA45 platforms. This guide is written for owners who have basic mechanical experience and are ready to take their vehicle's performance to the next level. We will walk you through everything: why the TD04HL-19T is an excellent choice, what additional parts you need, a detailed installation process, critical tuning steps, and the real-world performance gains you can expect—including a verified 50+ horsepower increase at the wheels.

Understanding the MHI TD04HL-19T Turbocharger

The MHI (Mitsubishi Heavy Industries) TD04HL-19T is a proven turbocharger platform originally found on various Subaru and Mitsubishi applications, but it has become a popular upgrade option for the M133 engine in the A45. Its compact size, quick spool characteristics, and ability to flow enough air for up to 450 horsepower make it a sweet spot for those seeking a substantial bump without sacrificing streetability.

Compared to the stock turbocharger, the TD04HL-19T features a larger compressor wheel (19T trim) and a slightly larger turbine housing. This combination allows for higher boost pressure at lower RPM and maintains airflow efficiency well into the mid-range. The result is a broader power band and a more linear delivery of torque, which translates to a much more responsive daily driver.

Key specifications of the MHI TD04HL-19T:

  • Compressor wheel: 19T billet or cast aluminum (depending on variant)
  • Turbine housing: Typically 6 cm² to 7 cm², matched to M133 exhaust manifold
  • Max sustainable boost: Up to 28-30 psi with proper tuning
  • Flow capacity: Approximately 440-470 horsepower on race fuel
  • Wastegate: Internal, adjustable for boost creep mitigation

For an in-depth look at the TD04HL family, check out Mitsubishi Turbo's official technical specifications.

Preparation and Required Parts

Before you begin the installation, gather all the necessary components. A turbo upgrade is rarely a standalone affair—supporting modifications are critical for reliability and performance.

Essential Hardware

  • MHI TD04HL-19T turbocharger (ensure correct flange pattern for M133 engine)
  • Upgraded intercooler (core should be at least 50% larger than stock)
  • High-flow downpipe (3-inch diameter recommended)
  • Larger fuel injectors (800-1000 cc/min or 40 lb/hr at 3 bar)
  • High-pressure fuel pump (or upgraded low-pressure pump for flex-fuel setups)
  • Cold air intake system (larger filter and smoother piping)

Tools and Safety Equipment

  • Socket set with extensions (metric 10mm to 18mm)
  • Torque wrench (ft-lb and in-lb)
  • Pry bars and picks for stubborn hoses
  • Oil catch pan (turbo coolant and oil will drain)
  • Fire extinguisher (safety first)
  • Jack stands or lift

Gaskets, Seals, and Fluids

  • Turbo-to-manifold gasket (copper or multi-layer steel)
  • Turbo-to-downpipe gasket
  • Oil return line gasket and crush washers
  • Coolant hoses and O-rings for the water lines
  • High-temperature thread locker (for bolts exposed to extreme heat)

For a comprehensive parts list and supplier recommendations, visit the AMG Performance forum where seasoned builders share their build sheets.

Installation Process

Step 1: Disconnect Battery and Drain Fluids

Always disconnect the negative battery terminal before working on the electrical system. Then drain the engine coolant (from the radiator petcock) and engine oil (from the oil pan). The turbo is water- and oil-cooled, so both systems will need to be open to avoid spills.

Step 2: Remove Stock Turbocharger

Access to the turbo on the A45 is tight; you will likely need to remove the intake manifold and throttle body for clearance. Start by disconnecting the charge air piping, then unbolt the exhaust manifold from the cylinder head (10 bolts, sequence matters). With the manifold free, you can unbolt the turbo from the manifold (4 bolts) and separate it. The oil feed line (banjo fitting) and coolant lines (two rubber hoses) must be disconnected. Take care not to drop debris into the open oil drain port.

Step 3: Prepare the New Turbo and Manifold

Inspect the MHI TD04HL-19T for any shipping damage. Install the oil restrictor in the feed port if one is not pre-installed (most aftermarket turbos require a restrictor to prevent over-oiling). Apply a thin layer of anti-seize to the wastegate actuator rod threads. Install new gaskets on the exhaust manifold and turbo flange. Use a torque wrench to tighten all fasteners to the manufacturer's specifications—typically 35-40 ft-lb for the manifold nuts and 30-35 ft-lb for the turbo-to-manifold bolts.

Step 4: Mount the New Turbo Assembly

Carefully position the exhaust manifold with the turbo attached back onto the engine block. Use new gaskets and torque in the correct sequence (center out). Reconnect the oil feed line with a new crush washer, the coolant lines, and the oil return line. Ensure the return line has a smooth downward slope—any kink or incline will cause oil pooling and premature turbo failure.

Step 5: Install Supporting Components

Now refit the upgraded intercooler, downpipe, and intake system. The downpipe should bolt directly to the turbo outlet flange—check for clearance against the subframe. Connect all boost pipes and secure them with T-bolt clamps. Install the boost gauge if you haven't already; it is essential for monitoring vacuum and boost during the break-in and tuning phase.

Step 6: Final Checks and First Start

Double-check all connections: oil lines, coolant lines, intake piping, and electrical connectors. Reconnect the battery. Prime the oil system by cranking the engine with the fuel pump fuse pulled (10 seconds, three times) to ensure oil reaches the turbo before it spins. Then install the fuse and start the engine. Let it idle for at least 5 minutes while inspecting for leaks. Gradually increase RPM to 2000-2500 and listen for any unusual noises. If everything sounds healthy, you are ready for the tuning phase.

Tuning for the MHI TD04HL-19T

The installation is only half the story. Without proper calibration, your new turbo will either leave power on the table or, worse, cause detonation. Tuning the M133 engine for the TD04HL-19T requires attention to fuel, timing, and boost control.

Selecting a Tuning Platform

Most A45 owners use either a flash tune (ECU remap) via tools like BHP or ECUtek, or a piggyback system like JB4. For a turbo this size, a custom ECU tune is strongly recommended. Flash tuning allows full control over fuel maps, ignition timing, camshaft phasing, and boost targets. If you are not a tuner yourself, find a reputable shop with experience on the M133 engine. ECUtek's official tuning guidelines provide a solid foundation for understanding how to approach the calibration.

Fuel System Upgrades

The TD04HL-19T can flow enough air to require 30-40% more fuel than stock. At a minimum, install larger injectors (800cc/min recommended) and a high-flow low-pressure fuel pump. If you plan to run ethanol blends (E30 to E50), a dedicated ethanol content sensor and adjustable fuel pressure regulator will be necessary. The stock fuel system maxes out around 400 horsepower; beyond that, you risk fuel starvation.

Boost Control Strategy

The internal wastegate on the TD04HL-19T is robust, but you must set the boost target carefully. Start with 22-24 psi on pump gas (91-93 octane) and monitor knock sensors. With a proper intercooler and water-methanol injection, you can push to 28-30 psi. Use a standalone boost controller or OEM-based boost control solenoid for consistent pressure. Avoid spike-and-ramp strategies—flat boost curves are safer and produce more predictable power.

Ignition Timing and Air-Fuel Ratios

Target an air-fuel ratio of 11.5:1 to 12.0:1 under boost to keep cylinder temperatures in check. Ignition timing should be conservative—no more than 12-14 degrees advanced at peak torque, tapering to 8-10 degrees at redline. Every motor is different, so use a dyno with wideband O2 feedback to dial in the final numbers. A good tuner will also adjust VANOS (cam timing) to optimize spool and top-end flow.

Data Logging and Fine-Tuning

After the base tune is loaded, take the car for a gentle drive. Log parameters: boost pressure, IAT, fuel trims, knock count, and exhaust gas temperature. Make small adjustments to the fuel map around peak torque to prevent lean spikes. The TD04HL-19T spools quickly, so pay attention to the transient fueling when you tip into the throttle. It often takes three to five revisions to get the tune perfect.

Expected Performance Gains

With a proper tune and supporting mods, the MHI TD04HL-19T delivers a clean 50-70 horsepower increase at the wheels over the stock turbo on the same fuel. On 93 octane, you can expect 380-400 whp from a stock internal A45; with E50, the number climbs to 440-460 whp. Torque jumps similarly, from around 330 lb-ft to 400-430 lb-ft at the wheels, all while maintaining a broad power curve.

But the real-world difference is in how the car feels. The stock turbo runs out of steam above 5500 RPM; the TD04HL-19T pulls hard all the way to 6800 RPM. Throttle response improves because the larger turbine housing reduces backpressure, allowing the engine to exhale more freely. On the street, you notice the car getting to highway speeds quicker with less effort.

These gains are consistent with data shared on AMG performance forums, where owners commonly report 50+ wheel horsepower increases from this specific swap.

Reliability Considerations

The M133 engine is robust, but pushing beyond 450 horsepower does require attention to heat management. Consider an upgraded radiator, oil cooler, and water-methanol injection to keep IATs low. The TD04HL-19T runs cooler than many larger turbos due to its efficient compressor map, but sustained high-speed track driving will test your cooling system. We recommend an oil analysis after the first 5000 miles to monitor bearing wear and fuel dilution.

Common Issues and Troubleshooting

Oil Leaks from Turbo

If you see oil dripping from the turbo after installation, the most likely culprit is an overly large oil feed hole. The restrictor should be 0.045-0.055 inches. Also verify that the oil return line is not kinked and that it runs downhill without any low points. If the return line is too short or incorrectly routed, oil will back up and leak past the piston ring.

Boost Creep

Some users report boost creep (boost rising uncontrollably) with the TD04HL-19T, especially on cars with a fully open exhaust and no catalytic converter. This happens because the wastegate port is not large enough to bleed off excess exhaust gas at high RPM. Solutions include porting the wastegate hole, using a higher-pressure wastegate actuator spring, or installing a boost controller that can manage bleed rate. Start with a 14-psi actuator spring and adjust from there.

Check Engine Light (CEL)

After the swap, you may trigger codes related to intake air temperature sensor values or post-cat O2 sensor faults. Most tuners will disable the secondary O2 sensors and adjust IAT sensor scaling. If the CEL persists, check that all electrical connections are secure and that the MAF sensor (if used) is oriented correctly.

Conclusion

The MHI TD04HL-19T turbo upgrade is a proven, reliable way to lift your A45 from quick to genuinely fast. By following the installation steps outlined here, investing in the correct supporting parts, and entrusting the tuning to a professional (or learning the ropes yourself), you can expect a trouble-free 50+ horsepower gain that transforms the car's character. The modification is well-documented in the community, so you are never alone during the process. Join the forums, ask questions, and enjoy the thrill of a perfectly sorted turbocharged AMG.

For parts and detailed build logs, Priority Performance offers complete TD04HL-19T kits for the M133 engine, including the necessary tune files. Drive safely and enjoy the extra boost.