Turbocharging the E60 M5: Achieving 700+ Hp with Custom Kits and Supporting Mods

The BMW E60 M5, powered by the naturally aspirated S85 V10, already delivers an intoxicating 500 horsepower from the factory. But for those who crave more – and many do – turbocharging opens a new realm of performance. With the right combination of a well-designed turbo kit, forged internals, and comprehensive supporting mods, 700+ wheel horsepower is not just possible; it’s repeatable and drivable. This guide expands on the core components, the essential upgrades, and the real-world considerations for building a 700+ horsepower E60 M5 that is both ferocious and reliable.

The S85 V10: Strengths and Weaknesses Under Boost

Before adding boost, it’s critical to understand the S85 engine. This 5.0-liter, 40-valve V10 features an aluminum block and heads, a forged steel crankshaft, and sintered connecting rods. The factory pistons are cast hypereutectic aluminum, which becomes a limiting factor at power levels above roughly 600–650 wheel horsepower. The cylinder walls are coated with an iron plasma spray (Alusil), which is durable but requires careful attention to fuel quality and tuning. The engine’s high-revving nature (8250 rpm redline) pairs well with turbocharging because it can sustain boost across a wider RPM band than a typical low-revving V8. However, the factory exhaust manifolds are restrictive and must be replaced with a turbo manifold. The main weaknesses for big power are the factory pistons and the rod bearings—common failure points in S85 engines even at stock power. Addressing these is non-negotiable for a 700+ HP build.

Choosing the Right Turbo Kit for the E60 M5

The market offers several excellent turbo kits, each with its own philosophy. Some are single-turbo kits designed for simplicity and packaging, while others are twin-turbo setups that mimic the OEM+ feel. When selecting a kit, prioritize quality of the cast or CNC-machined manifolds, the turbine housing material, and the quality of the included wastegate and blow-off valve. Look for kits that provide clear documentation and customer support.

  • Active Autowerke Gen 2 Turbo Kit – A well-known single-turbo (64mm or 67mm) kit with a cast stainless manifold and integrated wastegate. Supports 700–800 wheel horsepower on E85 with proper supporting mods. Uses a high-flow intercooler and polished charge pipes.
  • ESS Tuning VT2-600/725 – Though more famous for superchargers, ESS Tuning offers a twin-turbo system that uses two small-framed turbos (GT2252 or GT2871) for quick spool and linear power. Their systems include a custom intercooler and a proprietary tune.
  • VTT (Vargas Turbo Technologies) Single Turbo Kit – Designed for the S85, VTT’s kit features a precision journal bearing or ball bearing turbo (64mm to 76mm depending on power goal), a 4-inch downpipe, and a V-Band turbine outlet. Known for robust construction and scalability from 650 to 900+ wheel HP.
  • Custom Fabricated Kits – Many builders choose a custom kit using a bottom-mount or top-mount manifold and a turbo like a Garrett G35-1050 or a BorgWarner S366. This route requires an experienced fabricator but allows maximum packaging optimization and component choice.

Regardless of the kit, ensure it includes a properly sized intercooler core (bar-and-plate recommended), a high-flow intake with a large conical filter, and a complete set of gaskets and hardware. Active Autowerke’s E60 M5 turbo kit is a popular starting point for the 700 HP goal.

Essential Supporting Modifications for 700+ HP

Bolting on a turbo kit is only half the battle. The following modifications are required to ensure reliability and performance at this power level.

Engine Internals: Forged Pistons and Stronger Rods

As mentioned, the factory pistons are the weak link. For 700+ wheel horsepower, you need forged dished pistons from a supplier like JE, CP-Carrillo, or Mahle. Compression ratio typically drops from 12.0:1 to 9.5:1 or lower to allow for safe boost levels on pump gas or E85. It is also wise to replace the connecting rods with forged steel units (e.g., Carillo or K1 Technologies) if you plan to exceed 800 HP or use high boost. The stock rods are sintered and can bend under sustained high torque.

Fuel System Upgrades

700 HP requires roughly twice the fuel flow of the stock 500 HP engine. The factory fuel pump and injectors are inadequate. You will need:

  • High-flow fuel injectors – 1000–1300cc/min (or 96-105 lb/hr) injectors. ID1050x or Bosch EV14-based injectors are common. They must be tuned for proper spray pattern and dead times.
  • Upgraded fuel pump – A single Walbro 525 or dual in-tank pumps (e.g., DW400 pumps) to maintain fuel pressure under high load. Some kits require a return-style fuel system with an adjustable fuel pressure regulator.
  • E85 compatibility – If using flex fuel, ensure fuel lines, hoses, and o-rings are ethanol-rated. Stainless steel braided lines are recommended.

Intercooling and Charge Air Cooling

Maintaining low intake air temperatures (IATs) is crucial for sustained power and knock prevention. A front-mount intercooler (FMIC) with a core size of at least 20x12x3 inches and efficient bar-and-plate design is mandatory. Consider upgrading to a water-to-air intercooler if you want the shortest charge path and consistent temps during hot track sessions. Also, a larger radiator and an oil cooler upgrade (e.g., a Setrab or CSF unit) will help manage the additional heat from boosting.

Exhaust System

The turbo kit typically includes a downpipe. For the rest of the exhaust, a 3-inch or 3.5-inch cat-back system with high-flow catalytic converters (or no cats, depending on your region) reduces back pressure and allows the turbo to spool freely. Supersprint or Akrapovic systems are popular, but a custom 3-inch stainless system from a reputable shop will also work well. Note that the sound of a turbocharged V10 is different from the naturally aspirated scream; it becomes deeper and more aggressive.

Drivetrain Upgrades: Clutch, Transmission, and Differential

The E60 M5 uses the SMG III seven-speed automated manual transmission, which can handle around 600-650 wheel torque with stock clutch packs. For 700+ HP, the torque output (typically 650-750 lb-ft at the wheel) will exceed the stock SMG clutch’s capacity Turner Motorsport offers a heavy-duty clutch pack upgrade that can handle 800+ lb-ft. Alternatively, a full manual swap (e.g., using a ZF 6-speed from an E60 550i or a Tremec T56) is a common upgrade for enthusiasts who prefer mechanical control. The rear differential should also be upgraded: a limited-slip differential with higher friction clutches or an LSD insert (e.g., from KMP or Drexler) will help put the power down effectively.

Installation Process Overview

Installing a turbo kit on the E60 M5 is an intensive project requiring a lift, engine removal (in some cases), and professional fabrication skills if the kit is not fully bolt-on. The typical steps include:

  1. Drain coolant and oil, remove the intake manifold, exhaust manifolds, and the entire airbox.
  2. Remove the front bumper and crash bar for intercooler installation.
  3. Install the turbo manifold(s), turbocharger(s), and wastegate(s). Ensure proper clearance from the frame rails and subframe.
  4. Run the oil feed and drain lines to the turbo using stainless steel braided lines. A dedicated oil scavenge pump may be required for low-mount turbos.
  5. Mount the intercooler and charge pipes, ensuring all couplers are tight.
  6. Install upgraded fuel pumps, lines, and injectors.
  7. Reinstall the intake manifold with new gaskets. Wire in any necessary sensors (e.g., boost reference for MAP sensor).
  8. Install the downpipe and cat-back exhaust.
  9. Reattach the front bumper, fill fluids, and perform a leak test.

Most builders recommend having a professional shop with experience in the S85 complete this work. Improper oil drainage or boost leaks can lead to catastrophic failure.

ECU Tuning: The Key to Reliability and Power

The factory DME (Digital Motor Electronics) is not capable of controlling a turbocharged engine. You need a standalone ECU or a piggyback/flash solution from a company like ECU Tuning or a full Syvecs or Motec system. Many tuners use the stock DME reflashed with custom maps (e.g., using EcuTeck), which allows control of boost tables, fuel trims, and timing on the stock ECU. For a 700 HP build, a standalone is recommended for the flexibility to add flex fuel, boost-by-gear, and anti-lag. Key parameters to tune:

  • Air-fuel ratio (AFR): Aim for 11.5-12.0:1 under boost for pump gas, or 12.0-12.5:1 for E85.
  • Ignition timing: Timing must be reduced under boost; about 10-15 degrees at peak torque is typical.
  • Boost control: Use a MAC solenoid or electronic boost controller to map boost by RPM. For 700 HP on the S85, boost levels of 10-14 psi are typical on E85 with proper internals.
  • Fuel pressure and injector latency: Proper injector scaling and dead-time calibrations prevent lean conditions.

A professional dyno tune is essential. Expect to spend 2-3 days on the dyno achieving a safe, powerful calibration. Bimmer Performance is one of several well-known experts in S85 turbo tuning.

Dyno Results and Real-World Performance

A properly built 700 HP E60 M5 (measured at the wheels) will accelerate from 0-60 mph in about 3.2 seconds and trap mid-130s mph in the quarter mile. The power delivery is linear if the turbo is properly sized; a 64mm turbo will reach full boost around 3500 RPM and carry to redline. The car will feel much stronger than the stock M5 at every RPM, but the additional weight of the intercooler, larger radiator, and drivetrain upgrades will add about 50-80 pounds over the front axle. Using a 76mm turbo, the car can make 800+ wheel HP with a more aggressive tune. Keep in mind that at these power levels, traction becomes a challenge. Upgraded rear tires (295/30R19 or 305/30R19 with sticky rubber) and a rear LSD are strongly recommended.

Maintenance Considerations for a Turbocharged E60 M5

A 700 HP turbocharged E60 M5 requires diligent maintenance to avoid engine damage:

  • Oil changes: Use a high-quality 5W-50 or 10W-60 synthetic (Liqui-Moly or Motul) and change every 3,000 to 4,000 miles. The turbo adds heat and stress to the oil.
  • Cooling system: Monitor engine coolant temps and oil temps. An upgraded oil cooler and water pump (e.g., Stewart) are recommended. Inspect intercooler hoses for cracks annually.
  • Fuel system: If using E85, flush the system every few thousand miles to remove water contamination. Replace fuel filters regularly.
  • Boost leaks: Do a boost leak test every six months. A small leak can cause a lean condition under boost.
  • Rod bearings: Even with a built engine, the bearing clearances must be checked after the first 10,000 miles. Many S85s have spun bearings at stock power; with boost, this is even more critical. Use King or ACL race bearings.

Cost Considerations and Budgeting

Building a 700 HP E60 M5 is not a cheap endeavor. The total cost including the car, kit, internals, labor, and tuning typically falls between $35,000 and $60,000. A breakdown:

  • Turbo kit (with intercooler, downpipe): $6,000–$9,000
  • Forged pistons and rods + labor: $4,000–$6,000
  • Fuel system (injectors, pump, lines, regulator): $1,500–$3,000
  • ECU tuning (standalone or flash + dyno time): $2,000–$5,000
  • Drivetrain upgrades (clutch, LSD): $2,500–$5,000
  • Cooling upgrades (radiator, oil cooler, intercooler): $1,000–$2,000
  • Labor (600–1000 hours experienced shop): $10,000–$20,000

Conclusion

Turbocharging the E60 M5 to 700+ horsepower is an achievable goal that transforms an already legendary car into a true supercar-slaying machine. It requires careful selection of a high-quality turbo kit, a full engine rebuild with forged internals, a comprehensive fuel system, and professional tuning. The rewards are immense: a unique sound, mind-bending acceleration, and the satisfaction of owning a one-of-a-kind build. However, it is not a project for the faint of heart or wallet. Diligent maintenance and respect for the power are key to enjoying a 700+ HP E60 M5 for years to come.