Unlocking the True Potential of the Mercedes-AMG A45 with a BorgWarner EFR 8374 Turbocharger

The Mercedes-AMG A45 has long been celebrated as a benchmark in the hot hatch segment, offering a potent 2.0-liter turbocharged engine that delivers exhilarating performance straight from the factory. However, for owners who crave even more power, the aftermarket provides a path to significantly elevate the car's capabilities. One of the most compelling upgrades is the BorgWarner EFR 8374 turbocharger. This article explores the power gains this upgrade can deliver, the supporting modifications required, and what you can expect from a properly tuned A45 equipped with an EFR 8374.

Understanding the BorgWarner EFR 8374

The BorgWarner EFR (Engineered for Racing) 8374 is a state-of-the-art turbocharger designed for high-performance applications where response and efficiency are critical. Unlike many aftermarket turbos, the EFR 8374 incorporates advanced technologies that make it a standout choice for the A45's M133 and M139 engines.

Key Features of the EFR Series

  • Lightweight Gamma-Ti Turbine Wheel: Made from titanium aluminide for faster spool and reduced rotational inertia.
  • High-Flow Compressor: The 8374 features a 83mm compressor wheel and a 74mm turbine wheel, providing excellent airflow capacity.
  • Integrated Billet Wastegate: A cast-in, high-flow wastegate ensures precise boost control without the need for external gates in many applications.
  • Super Core Technology: Advanced aerodynamics deliver exceptional efficiency across a broad flow range.
  • Dual Ceramic Ball Bearings: Reduce friction and improve transient response compared to journal bearing turbos.

These features make the EFR 8374 particularly well-suited to the A45's high-revving, direct-injected engine. It can flow enough air to support well over 500 horsepower, while still spooling quickly enough to maintain daily drivability when paired with proper tuning.

Stock Performance of the Mercedes-AMG A45

Before diving into upgrade numbers, let's establish a baseline. The Mercedes-AMG A45 (2013-2019) came with the M133 engine producing 355-381 horsepower depending on the year and trim. The second-generation A45 (2020+) uses the M139 engine, factory rated at 382-416 horsepower in various states of tune. These cars are already quick, with 0-60 mph times in the low 4-second range.

However, factory turbochargers are sized for a broad power band and emissions compliance. The BorgWarner EFR 8374 opens up a much higher ceiling. With the M133 engine, stock turbo limits are typically around 400-420 wheel horsepower. The EFR 8374 can more than double that potential.

Power Gains from the BorgWarner EFR 8374 Upgrade

The question "How much power does the A45 upgrade with BorgWarner EFR 8374 add?" has a variable answer depending on several factors: the engine generation, fuel type, supporting modifications, and tuning approach. However, we can provide realistic estimates based on common builds.

Estimated Power Increase for M133 Engines

For the earlier M133-based A45, the EFR 8374 with proper supporting mods yields:

  • On pump gas (93 octane or 98 RON): 480-520 wheel horsepower, which translates to roughly 560-600 crank horsepower. That's an increase of 150-200 horsepower over stock.
  • On E85 or race fuel: 550-600 wheel horsepower, or approximately 650-700 crank horsepower. The torque curve also sees massive improvement, with 500+ lb-ft available from mid-range.

Estimated Power Increase for M139 Engines

The M139 engine has a stronger block and better head flow, enabling even higher output:

  • Pump gas: 520-560 wheel horsepower (600-650 crank).
  • E85: 600-650 wheel horsepower (700-750 crank). Some high-end builds have eclipsed 700 wheel horsepower with the EFR 8374 and extensive supporting mods.

The power gain is not just about peak numbers. The EFR 8374's efficiency means it can hold boost to redline, providing a much broader power band than many other large turbos. The result is a car that pulls relentlessly from 3,500 rpm all the way to 7,000+ rpm.

Supporting Modifications for a Reliable Build

Slapping a bigger turbo on a stock A45 is a recipe for failure. To safely handle the additional airflow and heat, you'll need a comprehensive set of supporting modifications. Here are the essentials.

Fuel System Upgrades

  • High-flow fuel injectors: Stock injectors quickly run out of capacity. Most A45 builds with the EFR 8374 use 1,000-1,300 cc injectors.
  • Upgraded high-pressure fuel pump (HPFP): Direct injection systems need more volume. A Turbosmart or similar HPFP upgrade is often required for E85.
  • Larger fuel lines and a return-style system: Some tuners recommend a Port Fuel Injection (PFI) kit to supplement the direct injectors, especially beyond 600 wheel horsepower.

Air Intake and Induction

The A45's stock airbox can become a restriction. A high-flow intake system like those from Eventuri or LDR Performance reduces intake restrictions and helps the turbo breathe.

Intercooler and Cooling

Boost air temperatures skyrocket with increased boost. A large front-mount intercooler (FMIC) is required. Additionally, upgrading the engine oil cooler and sometimes adding a water-methanol injection kit helps keep intake temperatures safe.

Exhaust System

  • Downpipe: A 3-inch or larger downpipe with a high-flow catalytic converter or catless design is essential to reduce backpressure.
  • Full exhaust: A 3-inch cat-back exhaust further improves flow and spool.

Engine Internals

For M133 engines aiming above 500 wheel horsepower, forged pistons and connecting rods are strongly recommended. M139 engines have forged components from the factory and can handle more, but at the 650+ wheel horsepower level, upgrading rods and pistons becomes good insurance.

Clutch and Transmission

The A45's dual-clutch transmission may need upgraded clutch packs for sustained high torque. A stronger clutch pack from Dodson Motorsport or SSP is common in high-power builds.

Tuning Considerations for the EFR 8374

The BorgWarner EFR 8374 requires professional tuning to unlock its full potential. A stock ECU map will not know how to control the larger turbo's airflow or fuel demands.

Choosing the Right Tuner

Look for tuners experienced with the M133/M139 platform. Renowned shops like Eurocharged Canada, LDR Performance, and AMR Performance have demonstrated consistent results. Typically, they use ECU tuning via the OBD2 port or bench flash, often with custom ROMs.

Boost Control and Mapping

The EFR 8374's integrated wastegate can be controlled electronically using the factory boost solenoid. However, many tuners switch to a Mac valve or a standalone boost controller for better resolution. Tuning focuses on target boost levels (20-30 psi) while managing ignition timing to avoid knock.

Safety and Reliability

Professional tuners set limits on timing and boost based on fuel quality and engine health. They also adjust the torque limits in the transmission control unit (TCU) to prevent clutch slip. With a good tune, these cars are reliable street machines, though they require more frequent maintenance (oil changes, spark plugs, etc.).

Real-World Performance Results

The power increase is dramatic. A stock A45 accelerates from 0-60 in the low 4-second range. An EFR 8374-powered car on pump gas can dip into the high 2-second range with proper tires and launch control. Quarter-mile times drop from the stock mid-12-second range to 10.5-11.0 seconds depending on power output and traction.

For example, a 2021 M139 A45 with an EFR 8374, full exhaust, and fresh intercooler on E85 recorded 621 wheel horsepower and 587 lb-ft on an independent dyno. It ran a 10.8 @ 131 mph in the quarter mile, with a 0-60 time of 2.9 seconds. The owner reported it retained drivability for daily use, with no abnormal heat issues.

Cost and Value Considerations

Upgrading to a BorgWarner EFR 8374 is not cheap. The turbo itself retails for around $2,000-$2,500. When you factor in supporting modifications, labor, and tuning, a complete build can range from $8,000 to $15,000. However, compared to other platforms, the A45 offers a strong ROI in terms of power per dollar.

For owners considering this route, it's essential to budget for maintenance and potential surprises. High-power builds often uncover weak points in the drivetrain. Still, many enthusiasts feel the transformation is worth it.

Alternatives to the EFR 8374

The BorgWarner EFR 8374 is a top choice, but there are alternatives. Precision Turbo's 5858 or 6266, Garrett GTX3582R, and the Pure Turbos upgrade for the A45's stock frame are options. However, the EFR 8374 stands out for its spool characteristics and build quality.

For those wanting a milder upgrade, a hybrid stock-frame turbo offers a more moderate gain (35-50% increase) without needing a full fuel system overhaul. But for maximum power, the EFR 8374 is the benchmark.

Conclusion

The BorgWarner EFR 8374 turbocharger can transform a Mercedes-AMG A45 from a quick hot hatch into a supercar-slaying machine. With power gains of 150-300 horsepower depending on fuel and modifications, this upgrade unlocks the M133/M139 engine's full potential. However, success requires a holistic approach: supporting modifications, professional tuning, and careful maintenance. For owners willing to invest, the result is a car that delivers breathtaking performance while remaining surprisingly drivable on the street. If you're chasing big numbers and even bigger smiles, the EFR 8374 is a proven path to power.

For more information on the BorgWarner EFR series, visit BorgWarner's official site. For build guides and community results, check forums like BenzBoost and MBWorld. For tuning services, consider reaching out to Eurocharged Canada or LDR Performance.