Understanding the F90 M5: A Paragon of Performance

The BMW F90 M5, introduced for the 2018 model year, redefined the executive sports sedan segment with its blend of luxury, technology, and brutal performance. At its core lies the S63B44T4 engine—a 4.4-liter twin-turbocharged V8 that, in stock form, delivers 600 horsepower and 553 lb-ft of torque. This power is channeled through an eight-speed automatic transmission and BMW’s M xDrive all-wheel-drive system, enabling a 0–60 mph sprint in just 3.2 seconds. However, for many enthusiasts, the factory output is merely a starting point. The robust architecture of the S63 engine, combined with a well-engineered forced-induction system, makes the F90 M5 an ideal candidate for bolt-on modifications. With a relatively modest set of upgrades, owners can reliably push power beyond 700 horsepower while retaining daily drivability. This guide provides a detailed cost breakdown and technical overview of the parts and labor required to achieve that milestone.

Key Modifications for Achieving 700 HP

Reaching the 700-horsepower threshold requires a strategic combination of parts that address airflow, fuel delivery, and engine management. Below is an expanded look at each essential modification, along with price expectations and performance gains.

ECU Tune (Engine Control Unit Optimization)

The single most impactful modification for any modern turbocharged engine is a proper ECU tune. The factory calibration is conservative to meet global emissions and reliability standards. A custom or off-the-shelf tune from a reputable company like BootMod3 or Dinan recalibrates fuel maps, ignition timing, and—most critically—boost pressure. On an otherwise stock F90 M5, a stage 1 tune alone can increase output to around 650–680 horsepower. To consistently hold 700 HP under all conditions, the tune must be matched with upgraded hardware. Cost for a high-quality flash tune or bench unlock ranges from $1,500 to $2,500, including the required software license and a remote or in-person dyno session.

High-Flow Downpipes

The F90 M5’s catalytic converters are a significant bottleneck. Replacing the factory downpipes with high-flow or catless versions reduces exhaust backpressure, allowing the twin turbos to spool faster and produce more top-end power. Many tuners require upgraded downpipes before applying a high-output calibration. Expect to pay $1,200 to $2,000 for a set from brands like Evolution Racewerks or Fabspeed. Note that catless downpipes may trigger a check-engine light without a tune, and some regions have emissions restrictions that make them illegal for street use.

Performance Intake System

Stock air intakes are designed for quiet operation and moderate airflow. Aftermarket cold-air intake systems, such as those from Eventuri or aFe Power, reduce restriction and lower intake air temperatures. While the horsepower gain from an intake alone is modest—typically 10–15 HP—it becomes crucial when combined with higher boost levels. Pricing for a complete carbon-fiber intake kit runs $500 to $1,000.

Upgraded Intercooler

One of the F90 M5’s known weaknesses is heat soak under sustained load. The factory charge air coolers (intercoolers) are adequate for stock power but quickly become heat-saturated during repeated pulls or track sessions. Upgraded intercoolers, like those from Wagner Tuning or VSR, feature larger cores and improved fin density. This keeps intake air temperatures lower, allowing the ECU to maintain timing advance and boost without knocking. A quality intercooler upgrade costs $1,000 to $2,000.

Performance Exhaust System

While not strictly necessary for reaching 700 HP, a cat-back exhaust system reduces backpressure further and shaves weight. More importantly, it unleashes the S63’s V8 soundtrack. Options range from axle-back systems to full cat-back with valves. Budget $1,500 to $3,000 for a system from Akrapovič, Remus, or AWE Tuning. Pairing this with the upgraded downpipes yields the full exhaust flow benefit.

Cost Breakdown Summary

The following list consolidates the estimated costs for each core bolt-on modification. Prices vary by brand, material (e.g., stainless vs. titanium), and whether you purchase new or used.

  • ECU Tune: $1,500 – $2,500
  • High-Flow Downpipes: $1,200 – $2,000
  • Performance Intake System: $500 – $1,000
  • Upgraded Intercooler: $1,000 – $2,000
  • Performance Exhaust System: $1,500 – $3,000

Additional Considerations That Impact Your Budget

Achieving 700 HP reliably involves more than just the five parts listed above. Several ancillary items and decisions can significantly affect the final total.

Labor Costs

If you plan to install the modifications yourself, you can save a substantial amount. However, the F90 M5 requires specialized tools and experience to remove downpipes (which are bolted to the turbos) and to properly pressure-test the system. Professional labor from a reputable BMW specialty shop typically runs 100–175 per hour. A full bolt-on installation can take 8–14 hours, resulting in labor charges of $1,000 to $2,500. Some shops also charge a dyno tuning session separately, adding $500 to $800.

Supporting Modifications for Reliability

At 700 HP, the factory fuel system—including the high-pressure fuel pump (HPFP) and injectors—may reach its limits, especially if you intend to use ethanol blends (e.g., E30 or E85). Upgrading to a stage 2 HPFP and larger injectors is often recommended. This can cost $1,000 to $2,000 for the hardware and a revised tune. Additionally, consider a low-pressure fuel pump upgrade for steady fuel delivery under high boost, which adds roughly $300–$600.

Tuning Software and Protections

Many ECU tuning platforms, such as BootMod3 or MHD, require a license that stays with the vehicle. That cost is included in the tune price range above. But some tuners also offer flexible fuel sensor kits, port injection controllers, or boost control modules. These extras can add $300–$1,000 depending on the complexity.

Warranty and Long-Term Reliability

Modifying your F90 M5 will almost certainly void the powertrain warranty if the car is still covered. Consider the cost of potential repairs—such as a blown turbo or transmission wear—which could run into the tens of thousands. Some owners purchase aftermarket warranties that cover modified cars, but these are rare and expensive. A more pragmatic approach is to set aside a contingency fund of $2,000–$5,000 for unexpected repairs or a new clutch pack if you frequently race the car.

Tuning Strategy: Remote vs. Dyno vs. Custom

An off-the-shelf tune from a known vendor is the most economical way to reach 700 HP. However, a custom dyno tune performed by a skilled tuner on your specific car often yields safer, more consistent power. The difference in cost is roughly $300–$800. For a build pushing the stock turbos to their limit, a custom tune is strongly advised to avoid detonation or overspin.

Total Estimated Cost to Build a 700 HP F90 M5

Combining the core mods, labor, and supporting components, the total investment can vary widely based on your choices. Below are two realistic scenarios.

Scenario 1: Budget-Conscious DIY Build

  • ECU Tune: $1,800 (custom remote flash)
  • Downpipes: $1,400 (catted high-flow, used)
  • Intake: $600 (chosen brand on sale)
  • Intercooler: $1,200
  • Exhaust: $1,800 (used cat-back)
  • Fuel system: $1,200 (HPFP alone)
  • Installation: $0 (DIY)
  • Total: ~$8,000

Scenario 2: Full Turnkey Shop Build with All Supporting Mods

  • ECU Tune: $2,500 (custom dyno tune + license)
  • Downpipes: $2,000 (new, catless, ceramic coated)
  • Intake: $1,000 (Eventuri CF)
  • Intercooler: $2,000 (Wagner top mount)
  • Exhaust: $3,000 (Akrapovič titanium)
  • Fuel system: $2,500 (HPFP + injectors + LPFP)
  • Labor: $2,500
  • Total: ~$15,500

Note that neither scenario includes a contingency fund for repairs. Many owners spend between $7,000 and $15,000 to reach a safe, reliable 700 HP. Spending beyond $15,000 typically moves into upgraded turbos or additional cooling systems.

Conclusion

Building a 700-horsepower F90 M5 with bolt-on modifications is entirely feasible and delivers an exhilarating driving experience. The key is to select high-quality parts, pair them with a custom tune, and remain realistic about labor and supporting upgrades. While the initial investment of $8,000 to $15,000 may seem steep, the result is a sedan that rivals supercars in acceleration while maintaining the everyday usability that makes the M5 legendary. Always research your specific year and build date—early 2018 cars have different boost control strategies—and consult with experienced tuners to maximize both power and longevity.