Cost Breakdown: Upgrading Your B58 M240i to 500 HP

The BMW M240i with the B58 engine has become a darling of the tuner community, and for good reason. This turbocharged inline-six delivers a robust factory output, yet its closed-deck design, robust internals, and advanced thermal management make it a prime candidate for substantial horsepower gains. Pushing the car to 500 wheel horsepower is not only achievable but can be done reliably with the right combination of hardware and software. This guide provides a detailed, line-item cost breakdown of the essential components—featuring HKS turbochargers, ETS intercoolers, and JB4 tuning—along with the supporting modifications required to reach that 500 hp target. We'll explore why each part matters, what installation entails, and how to budget realistically for a finished build.

Understanding the B58 Engine’s Potential

Before diving into the parts list, it is worth understanding why the B58 family responds so well to tuning. The engine employs a forged steel crankshaft, forged connecting rods, and a closed-deck cylinder block—features typically found in high-performance variants. In factory form, the M240i produces approximately 335 horsepower at the crank. With a simple piggyback tune like the JB4, owners often see 370–390 whp on pump fuel. Upgrading the turbocharger and intercooler, along with supporting mods, allows the engine to breathe more freely and sustain boost pressure without heat soak. The result is a smooth, linear power curve that rivals purpose-built sports cars.

It is crucial to note that the B58’s fuel system is capable up to around 500 wheel horsepower on the stock high-pressure fuel pump (HPFP). Beyond that, a port injection or upgraded HPFP becomes necessary. For the 500 hp target we are discussing, the stock HPFP is sufficient provided you are using quality fuel and a conservative tune.

Key Components for the 500 HP Build

The following three components form the core of this upgrade path. Each addresses a specific bottleneck in the stock system: turbocharger flow, charge air cooling, and engine management.

HKS Turbocharger Kit

The HKS turbocharger kit is a popular choice among B58 owners looking for a substantial increase in airflow without sacrificing spool characteristics. The kit replaces the factory twin-scroll turbo with a larger, single-scroll unit that features a billet compressor wheel and a larger turbine housing. HKS is known for their precision engineering and reliability, making this kit a credible option for daily-driven cars that see track time.

  • Cost: $3,500 (kit includes turbocharger, oil and coolant lines, gaskets, and heat shield)
  • Installation: $800 (professional labor, ~6–8 hours)
  • Why HKS? Compared to other options like the Pure Turbo Stage 2, the HKS kit offers a more straightforward installation with no need to send in your core. It also retains the stock location, simplifying plumbing.

Alternatives: The Pure Turbo Stage 2 is a direct bolt-on upgrade that uses the factory housing and can produce similar power levels at a slightly lower cost ($2,800). However, the HKS kit is often preferred for its proven track record in the Japanese market and its ability to flow enough air for 500 wheel horsepower on E85 blends.

ETS Front Mount Intercooler

As boost levels rise, charge air temperatures climb rapidly. The stock intercooler is a bar-and-plate design that is adequate for factory output but quickly becomes a bottleneck under sustained load. An ETS (Extreme Turbo Systems) front mount intercooler is a massive step up: it uses a much larger core with cast end tanks and a fin density optimized for the B58’s airflow requirements. The result is intake air temperatures that stay within 10–15°F of ambient, even during multiple back-to-back pulls.

  • Cost: $1,200 (intercooler, charge pipes, hardware)
  • Installation: $400 (2–3 hours labor)
  • Why ETS? ETS intercoolers are widely regarded as some of the most effective on the market for the B58. The kit includes upgraded charge pipes that eliminate the plastic factory pipes, which are prone to cracking under higher boost.

Alternatives: Wagner Tuning, CSF, and ARM offer comparable intercoolers. The ETS unit is chosen here for its price-to-performance ratio and direct-fit design. Some owners opt for a cold-side charge pipe upgrade only, but the full intercooler replacement is recommended for optimal thermal management.

JB4 Tuning Module

The JB4 from Burger Motorsports is a user-friendly, plug-and-play tuning module that connects to the DME (engine computer) via the OBD-II port and several sensor taps. Unlike a full ECU flash, the JB4 intercepts and modifies sensor signals to increase boost pressure and adjust fueling. It offers multiple maps for different octane levels, including a Map 2 (93 octane), Map 5 (auto-learning), and Map 6 (custom). The JB4 also includes a data logging feature that is invaluable for fine-tuning your build.

  • Cost: $600 (JB4 module, Bluetooth adapter optional for $50)
  • Installation: $100 (DIY install is straightforward; professional install is minimal)
  • Why JB4? For owners who want adjustability without a permanent flash, the JB4 is ideal. It can be removed before dealer visits and allows for real-time map switching. It also integrates well with other modifications like methanol injection.

Note: As power levels approach 500 wheel horsepower, many tuners recommend a custom ECU flash (e.g., MHD or BM3) for more precise fuel and timing control. However, the JB4 can still achieve this target with proper supporting mods and quality fuel. The cost of a flash tune would add another $600–$800 and require a laptop or mobile app.

Supporting Modifications – The Foundation of Reliability

No turbo upgrade is complete without addressing the intake and exhaust sides. The stock airbox and exhaust are restrictive at this power level, and the fuel system may require minor upgrades to keep up with increased demand.

High-Performance Exhaust System

A cat-back exhaust reduces backpressure and unlocks some horsepower, but the real bottleneck is the downpipe. For 500 hp, a catted or catless downpipe is essential. Many owners pair a downpipe with a free-flowing cat-back system to fully realize the turbo upgrade’s potential.

  • Cost: $1,000 (catted downpipe and cat-back, or full turbo-back system)
  • Installation: $300 (downpipe installation requires careful work with O2 sensors)

Popular brands include AWE, Remus, and Active Autowerke. A catted downpipe is recommended for those who need to pass emissions inspections.

Cold Air Intake

The factory intake is efficient for stock power, but a high-flow intake reduces restriction and provides a more direct airflow path. It also produces a satisfying induction noise that complements the turbo whistle.

  • Cost: $300 (drop-in filter or full intake kit)
  • Installation: $100 (DIY, 30 minutes)

Brands like MST, Eventuri, and Dinan are well-regarded. The MST V3 is a popular choice for its heat shield design and maintenance-free filter.

Upgraded Fuel Pump

While the stock HPFP is capable of 500 whp on pump gas, switching to an ethanol blend (E30 or E50) can stress it. An upgraded HPFP, such as the XDI-35 or Fuel-It!, adds headroom and protects against fuel pressure drop at high boost.

  • Cost: $500 (HPFP upgrade)
  • Installation: $200 (moderate difficulty; requires removal of intake manifold)
  • Important: If you plan to run only 93 octane, you can skip this upgrade and save $700. However, for the advertised 500 hp target, especially on an ethanol blend, the fuel pump is a worthwhile safety measure.

Total Cost Summary

Here is the full breakdown, including parts and professional installation for all components. Prices are estimates based on current market values and may vary by region and shop labor rates.

  • HKS Turbocharger Kit: $4,300
  • ETS Front Mount Intercooler: $1,600
  • JB4 Tuning Module: $700
  • High-Performance Exhaust (downpipe + cat-back): $1,300
  • Cold Air Intake: $400
  • Upgraded Fuel Pump: $700

Estimated Grand Total: $9,000

This figure includes parts and labor. If you perform the intake, exhaust, and JB4 installation yourself, you can save approximately $500–$600. Conversely, if you opt for a full custom tune in place of the JB4, add $600–$800. A reputable shop will also account for fluids, gaskets, and shop supplies, so budget an additional $200–$300 for incidentals.

Installation Considerations – DIY vs. Professional

Some components, like the intake and JB4, are straightforward enough for a mechanically inclined owner with basic tools. The turbocharger and intercooler, however, require specialized knowledge and equipment. Removing the factory turbo involves working in a tight engine bay and carefully disconnecting coolant and oil lines. A lift and turbo socket set are nearly mandatory. Many owners prefer to have a shop handle the turbo and intercooler installation to avoid costly mistakes and to ensure proper torquing of fasteners.

If you are considering a DIY approach for the turbo, invest in a quality repair manual and watch several detailed video guides from reputable sources like the forums at Bimmerpost. Having a second set of hands is also beneficial.

Real-World Performance Results

With the combination described above, on 93 octane fuel, a B58 M240i typically puts down 480–500 wheel horsepower on a Dynojet dynamometer. Ethanol blends (E30–E50) can push that number to 530–540 whp, but that requires stronger fuel system modifications and a custom tune. The throttle response is sharp, and the car pulls hard through the entire rev range. Many owners report 0–60 mph times in the 3.2–3.5 second range with sticky tires, and the quarter-mile drops into the low 11s or high 10s.

It is important to note that achieving exactly 500 whp depends on variations in dyno, elevation, fuel quality, and ambient temperature. The goal is to build a system that is capable of that output, rather than chasing a specific number. Reliability should remain the priority.

Alternatives and Upgradability

If your budget is tighter, you can still see significant gains with a smaller investment. A stage 1 tune (JB4 or flash) plus a downpipe and intercooler will yield around 400–420 whp for roughly $2,500. That is a 100 whp increase over stock for a fraction of the cost. The full build described here is for those who want the ceiling to be 500 hp and are willing to invest in the turbo upgrade as the centerpiece.

For future expansion, the B58 platform responds well to port methanol injection and water-methanol kits, which can support 600+ whp with a built transmission and stronger rods. However, that is beyond the scope of this guide.

External Resources

Conclusion

Upgrading your B58 M240i to 500 horsepower is a rewarding project that transforms an already enjoyable sports coupe into a genuine street predator. By selecting proven components like the HKS turbocharger, ETS intercooler, and JB4 tuning module, and by supporting those parts with a properly sized exhaust, intake, and fuel system, you can achieve reliable power without pushing the engine beyond its design limits. The total cost of about $9,000 (parts and professional installation) is reasonable when compared to the price difference between the M240i and a new M2 Competition, and the performance can easily exceed that of much more expensive cars. Plan your build carefully, use quality parts, and enjoy the process of unlocking the full potential of BMW’s fantastic B58 engine.