The BMW M4, equipped with the S55 engine, is already a formidable performance machine straight from the factory. However, for enthusiasts seeking significantly higher output, the turbocharger system is the primary bottleneck. Upgrading the turbos is the most effective path to substantial horsepower gains. Among the aftermarket options, the BorgWarner EFR 7670 turbocharger has emerged as a favorite for M4 owners who want a balance of quick spool, high flow capacity, and advanced engineering. This article provides an authoritative breakdown of the horsepower gains you can expect from the BorgWarner EFR 7670 on an S55-powered M4, the factors that influence those gains, and what it takes to unlock the full potential of this turbo upgrade.

What is the BorgWarner EFR 7670 Turbocharger?

The BorgWarner EFR (Engineered For Racing) series represents a generation of turbochargers designed from the ground up for performance applications, using motorsport-derived technology. The EFR 7670 is a specific frame size within the series, featuring a 67.4mm compressor inducer and a 70.2mm turbine exducer. It is engineered to handle airflows capable of supporting over 700 wheel horsepower on the S55 platform with the right supporting modifications.

Key technological features that set the EFR 7670 apart include:

  • Advanced γ-Ti (Gamma Titanium Aluminide) Turbine Wheel: This lightweight material drastically reduces rotational inertia, allowing the turbo to spool faster than comparably sized turbos with stainless steel or Inconel wheels. It also offers excellent high-temperature durability.
  • Dual Ball Bearing System: Unlike journal bearings found in many stock turbos, the EFR uses a dual ball bearing cartridge that minimizes friction. This results in quicker spool, faster transient response, and better oil flow characteristics.
  • Integrated Bypass Valve and Wastegate: The compressor cover includes an integrated recirculating bypass valve (BOV), and the turbine housing features an integrated, high-flow wastegate. This simplifies installation and improves boost control reliability.
  • Cast Stainless Steel Turbine Housing: The use of investment-cast 304L stainless steel in the turbine housing ensures durability under extreme thermal stress while offering superior flow characteristics compared to cast iron units.
  • Marine-Grade Aluminum Compressor Housing: The compressor housing is made from marine-grade aluminum for corrosion resistance and weight savings.

These design choices make the EFR 7670 a popular choice for tuners who demand both high peak power and excellent drivability. Learn more about BorgWarner's EFR technology here.

Horsepower Gains on the BMW M4: Stock vs. Upgraded

The stock S55 engine in the BMW M4 (F82/F83) produces approximately 425 horsepower at the crank. On a dyno, stock M4s typically put down around 370 to 390 wheel horsepower (whp). With the BorgWarner EFR 7670 turbo upgrade, along with proper tuning and essential supporting modifications, owners can expect a significant increase in power.

Real-world results from reputable BMW tuners show that a fully dialed-in EFR 7670 system typically produces 560 to 620 wheel horsepower on pump gas (93 octane) at moderate boost levels (around 20-22 psi). On race fuel or ethanol blends (E85), that figure climbs to the 650 to 720 whp range. This represents a gain of roughly 170 to 330 wheel horsepower over a stock M4—converting the car into a genuine street weapon capable of low 10-second quarter-mile times.

It is important to note that these gains do not come from the turbo alone. They are the result of a comprehensive system change. The EFR 7670 has the capacity to flow enough air for those numbers, but the engine management system and fuel system must keep pace. Read about a typical EFR 7670 kit for the S55 at BimmerWorld.

Dyno Comparison: Stock vs. EFR 7670 (Estimates)

  • Stock M4: 375-390 whp / 400-420 lb-ft tq (on pump gas)
  • EFR 7670 (Pump Gas): 560-620 whp / 540-600 lb-ft tq
  • EFR 7670 (E85 / Race Fuel): 650-720 whp / 600-670 lb-ft tq

The torque curve is also notably wider and flatter than the stock turbos, with the EFR 7670 reaching full boost earlier than many other upgraded units of similar peak capacity, thanks to the low-inertia titanium turbine wheel. This means the car pulls harder from mid-range RPMs all the way to redline.

Key Factors That Influence Final Power Output

The horsepower you ultimately achieve with an EFR 7670 turbo on your M4 is not a fixed number—it depends on several critical variables. Achieving the higher end of the power spectrum requires careful attention to each of these elements.

Tuning and Calibration

The engine control unit (ECU) tune is the single most important factor. A skilled tuner will optimize fuel delivery, ignition timing, boost pressure, cam timing, and wastegate duty cycles to match the turbo's flow characteristics. The S55's Bosch ECU is complex, and you will need a custom flash tune (often using tools like Bootmod3 or MHD) to unlock the turbo's potential. Poor tuning can result in sub-optimal power or even engine damage.

Fuel Quality and Octane

Higher octane fuel allows for more aggressive ignition timing and higher boost levels without detonation. Pump gas (93 AKI) will limit you to the 560-620 whp range. To safely push beyond 650 whp, you will need either a high ethanol blend (E30-E85) or race fuel. Ethanol also provides a cooling effect in the combustion chamber, which helps with thermal management on high-boost setups.

Boost Pressure

The EFR 7670 is capable of handling boost pressures from 15 psi all the way to 30+ psi. However, the S55's direct injection and stock closed-deck block are robust, but the stock pistons and rods have limits. Most safe daily-driver tunes run 20-22 psi. Track-focused or dedicated drag setups may push 25-28 psi, but this often requires upgraded fuel system and careful monitoring.

Supporting Modifications

The turbo cannot work in isolation. The engine must be able to feed it clean, cool air, expel exhaust gases efficiently, and deliver enough fuel. Key supporting mods are discussed in detail in the next section.

Supporting Modifications You Should Consider

Installing an EFR 7670 turbo on your M4 without supporting modifications is like putting a high-performance carburetor on a stock engine—it won't perform properly. To maximize your investment, consider these upgrades as part of the package.

Fuel System Upgrades

The stock S55 high-pressure fuel pump (HPFP) and low-pressure pump can run out of capacity beyond 600 whp. For E85 or high boost, you will likely need:

  • Upgraded low-pressure fuel pump (e.g., Walbro 525 or similar)
  • Larger fuel injectors (ported injection or upgraded direct injectors are options)
  • Secondary port injection manifold for very high power goals

Intake and Charge Air Cooling

The EFR 7670 moves a lot of air. The stock air intake may be a restriction. A high-flow intake system with a larger filter is recommended. More importantly, the intercooler must be upgraded. The stock charge air cooler can heat-soak quickly under high boost. A high-capacity stepped intercooler or a front-mount intercooler (if using a custom setup) is essential to keep intake air temperatures (IATs) in check.

Exhaust System

The turbo's turbine side needs to flow freely. A full exhaust upgrade, including a high-flow downpipe (catted or catless), a mid-section, and an axle-back exhaust, will reduce backpressure and help the turbo spool more efficiently. A catless downpipe offers the most flow but may not pass emissions in some regions.

Engine Internals and Cooling

For power levels up to around 650 whp, the stock S55 bottom end is generally considered reliable with a good tune. Beyond that, forged pistons and connecting rods are recommended to prevent bending rods under high cylinder pressure. Additionally, an upgraded oil cooler and a larger radiator may be necessary for extended track use.

Installation Considerations

While the EFR 7670 can be installed by skilled DIY mechanics, it is not a straightforward bolt-on job. The installation involves significant work. Key considerations include:

  • Custom Downpipe Fabrication: The EFR 7670 uses a T4 or T3 flange (the kit you purchase will dictate this). You will need a custom downpipe or a kit-specific downpipe to connect the turbo to your exhaust.
  • Oil and Coolant Lines: The stock turbo lines will not fit. You will need to fabricate or purchase a braided stainless steel oil feed, oil return line, and coolant lines. Ensure proper alignment to avoid leaks.
  • Intercooler and Piping: Most EFR kits for the S55 use a custom front-mount intercooler with new charge pipes. This requires removal of the front bumper and careful routing.
  • Wastegate Actuator Setup: The integrated wastegate needs to be properly plumbed into the intake system or vented to atmosphere, depending on the tune.
  • Tuning Immediately After Install: The car will not run correctly without a custom flash. Do not attempt to drive the car with a stock tune—the engine will run lean and very lean conditions can cause catastrophic damage.

Given the complexity, professional installation by a shop experienced with S55 and BMW turbo upgrades is highly recommended. Check out an EFR 7670 kit with installation guidelines at ECS Tuning.

Real-World Dyno Results and User Feedback

Online forums such as Bimmerpost and enthusiast groups have documented numerous EFR 7670 builds. Common feedback includes:

  • Spool is noticeably faster than many other upgraded turbos in the 700+ whp class. Full boost often arrives by 3500-3800 RPM, compared to 4000+ RPM with larger frame turbos.
  • Mid-range torque is substantial, making the car feel much stronger than the peak numbers suggest.
  • Response is crisp, with minimal lag between gear changes when using dual clutch transmission (DCT).
  • Dyno results show smooth power curves that build linearly, rather than a sudden surge of boost.

Some owners note that on pump gas, the EFR 7670 may not reach its full potential, and that the turbo is "capped" by fuel octane. Switching to E85 or a methanol injection kit often reveals the turbo's true capability. Read a detailed build thread with dyno charts on Bimmerpost.

Cost Analysis and Value

Installing an EFR 7670 turbo is not cheap. The turbocharger itself retails for around $1,800 to $2,200, but a complete kit including the turbo, intercooler, piping, and necessary hardware costs approximately $4,000 to $6,000. Add in the cost of supporting modifications (exhaust, fuel system, tuning), and the total budget for the project often falls between $8,000 and $15,000 depending on the scope of work and whether you do the labor yourself.

Compared to other 700+ whp turbo solutions like twin-scroll conversions or Pure Stage 2+ turbos, the EFR 7670 offers competitive spool and peak power, often at a lower total system cost than a fully built twin-turbo setup. For the M4 owner who wants a proven, reliable single-turbo conversion (or twin-scroll upgrade on the factory twin-turbo arrangement), the EFR 7670 represents excellent value for the horsepower per dollar.

Reliability and Longevity

BorgWarner designed the EFR series with durability in mind. The dual ball bearing cartridge is less sensitive to oil flow issues than journal bearings, though it still requires a clean oil supply and proper cooling. The titanium turbine wheel resists creep at high exhaust gas temperatures, and the stainless steel housing resists corrosion and cracking.

However, reliability of the overall setup depends heavily on installation quality and tuning. Common failure points with aftermarket turbo setups include:

  • Oil leaks from poorly fitted lines
  • Boost control issues from incorrect wastegate spring setup
  • Overheating due to insufficient intercooler capacity
  • Detonation damage from aggressive tuning on low-octane fuel

With a skilled tuner and quality installation, the EFR 7670 itself is a long-lasting component. Many owners report 30,000+ miles without issue. Routine oil changes and occasional boost leak checks will help maintain performance.

Conclusion

The BorgWarner EFR 7670 turbocharger is a proven upgrade for the BMW M4's S55 engine, capable of adding 170 to 330 wheel horsepower over stock. When paired with proper tuning, fuel system upgrades, and supporting modifications, it transforms the M4 into a high-600 to low-700 wheel horsepower machine that retains excellent street manners and spool characteristics. The turbo's advanced engineering—titanium turbine wheel, dual ball bearings, and integrated wastegate—make it a standout choice in a crowded aftermarket landscape.

If you are serious about extracting maximum performance from your M4 while maintaining drivability, the EFR 7670 is a compelling option. Just be prepared for the associated costs and the need for professional installation and calibration. With the right approach, your M4 will deliver a driving experience that rivals far more exotic machinery.