BMW B58 Engine Guide: Tuning, Best Mods & Reliability

What is the BMW B58 engine?

The BMW B58 engine has in many independent BMW car experts opinions been described as one of the best engines BMW has ever made. The BMW B58 engine has firmly established itself as one of the standout performance engines of the modern era. It was introduced in 2015 as the successor for the N55. While the N54 and N55 proved successful, tightening emissions regulations, increasing efficiency demands, and the need for greater performance potential meant BMW required a more advanced straight-six engine platform moving forward.

The B58 is a 3.0-litre turbocharged straight-six developed as part of BMW's modular engine range, using a 500cc-per-cylinder design shared across its B-series engines. The B58 replaced the N55 as BMW looked to improve efficiency, emissions, refinement and performance, while developing a more versatile range of engines that could be used across a wider variety of vehicles.

But the figures on paper only tell part of the story. The B58 quickly earned a reputation for delivering smooth, effortless power while being remarkably receptive to tuning. Its strong underlying architecture means there is considerable headroom beyond the factory output, and relatively modest modifications can deliver gains that would have required far more work on previous generations.

That combination of strength, reliability and tuning potential has made the BMW B58 engine a firm favourite within the BMW tuning community. It takes much of what enthusiasts loved about its predecessor the N55 and builds on it, providing a stronger foundation for making power without losing the refinement and everyday usability expected from a modern BMW.

Nearly a decade on from its introduction, the B58 is no longer simply regarded as a good BMW engine. It has become the benchmark against which many modern turbocharged six-cylinder engines are measured, and one of the most exciting platforms to modify.

Which cars have the BMW B58 engine?

Since its introduction in the BMW 340i in 2015, the BMW B58 engine has gone on to power an enormous range of models. Early applications included the F30 340i, F20 M140i, F22 M240i and F32 440i, before the B58 made the jump into BMW's newer G-Series cars including the G20, G22 and G29. Today, different generations of the engine can be found in everything from the M240i, M340i and M440i to the Z4 M40i, 540i, 740i and 840i, as well as SUVs - X3, X4, X5, X6 and X7. Few modern BMW engines have been used quite so extensively.

Perhaps the biggest endorsement of the B58, though, is that other manufacturers wanted it too. Toyota famously chose BMW's 3.0-litre straight-six for its GR Supra, while INEOS selected the B58 petrol engine for its Grenadier 4x4 and Quartermaster pick-up. British sports car manufacturer Morgan also adopted the B58 for its Plus Six in 2019 and has continued its relationship with BMW's straight-six in newer models including the Midsummer and Supersport. Even low-volume German sports car manufacturer Boldmen has used the B58 in its CR4 roadster.

That is quite impressive for one engine. From BMW performance cars and luxury saloons to the GR Supra, hand-built Morgan sports cars and a rugged INEOS off-roader, the B58 has proven remarkably adaptable. More importantly for enthusiasts, its combination of performance, reliability and tuning potential means it works just as well as the starting point for a modified road car as it does powering one straight from the factory.

Why is the B58 so good for tuning?

Technical deep dive: Closed-deck block design, forged crankshaft and connecting rods, heat exchanger design, and fuelling efficiency.

B58 Gen 1 vs Gen 2: What's the Difference?

The BMW B58 engine has undergone several revisions since its introduction, but for tuning and aftermarket parts, these are most commonly grouped into B58 Gen 1 and B58 Gen 2. These aren't BMW's official names, but they have become the standard terminology used throughout the tuning community. Gen 1 referred to as B58 Gen 1 and Gen 2 is also commonly referred to as the B58TU, or Technical Update, reflecting the significant changes BMW made to the original B58 design.

The original B58 first appeared in 2015, replacing the N55 across a growing number of BMW models over the following years. For UK enthusiasts, the best-known Gen 1 cars are the M140i, M240i, 340i and 440i – the models that really established the B58 as a serious tuning platform.

BMW introduced the B58-powered M140i and M240i from July 2016, replacing the N55-powered M135i and M235i respectively. These cars, alongside the 340i and 440i, have since become some of the most popular B58 tuning platforms.

BMW's first major technical update to the B58 began appearing towards the end of the 2010s. Commonly referred to by tuners as B58 Gen 2 or B58TU, the revised engine brought significant changes to the fuel system, cylinder head, exhaust manifold, cooling and timing system.

The B58TU is particularly important from a tuning perspective because BMW didn't simply increase the factory output. It revised a number of the components that determine how the engine responds as power increases, particularly its cooling and fuelling systems. This means identifying whether you have a Gen 1 or Gen 2 B58 is important before choosing a remap or supporting performance parts.

B58 ECU Lock & FEMTO Unlock Requirements

Before tuning a B58, there is one important detail to check: when the car's DME (Digital Motor Electronics) was manufactured. BMW introduced additional security to Bosch MG1 DMEs produced from around June 2020 onwards, which prevents them from being unlocked using the conventional bench methods available for earlier cars.

On most pre-June 2020 B58s, a locked DME can be removed from the car and bench unlocked by a suitably equipped tuner. Once unlocked, compatible tuning software can then be used to flash maps and make future changes without repeating the original unlocking process.

For DMEs manufactured from around June 2020 onwards, things are different. These later units use additional security that conventional bench unlocking cannot bypass. If you want to run an ECU tune using platforms such as bootmod3, MHD or compatible EcuTek solutions, the DME will typically need to be removed and sent to a company like FEMTO, Autotuner, RPM or another DME unlocking specialist for unlocking before it can be flashed with compatible tuning software.

Importantly, this cut-off relates to the manufacture date of the DME itself, not simply the registration year of the car. A 2020 or 2021 car shouldn't automatically be assumed to need a DME unlock, just as the model year alone isn't enough to determine whether a conventional bench unlock is possible. Checking the DME before planning your B58 remap is the safest way to establish which unlocking process your car requires.

An unlock doesn't tune the engine or increase power on its own. It simply unlocks the DME so that compatible tuning software can be installed. Once unlocked, you can then move forward with the appropriate B58 Stage 1, Stage 2 or custom calibration for your setup.

How much power can a BMW B58 make?

One of the biggest attractions of the BMW B58 engine is just how much additional power can be unlocked without opening the engine. Depending on the model and B58 generation, factory output typically sits between around 320 and 380+ bhp, but there is considerable headroom beyond that. A simple ECU remap can take the B58 well beyond 400 bhp, while the right combination of supporting hardware, fuelling and turbo upgrades can push a properly built setup beyond 600 bhp.

As a rough guide, this is what you can expect at each stage:

For most road cars, Stage 1 is arguably the sweet spot. The standard B58 responds extremely well to software, with a quality remap capable of delivering a substantial increase in power and torque without requiring major hardware changes. It is one of the reasons B58 tuning is so accessible – you don't need to replace half the engine to make a genuinely fast car.

Moving to B58 Stage 2 typically introduces a freer-flowing downpipe alongside revised software, reducing exhaust restriction and allowing the turbo to operate more effectively. Depending on the generation, fuel quality and calibration, a Stage 2 B58 can comfortably move into the mid-to-high 400 bhp region.

Beyond this, fuelling starts to become increasingly important. Stage 2+ setups often combine an upgraded high-pressure fuel pump with an appropriate ethanol blend such as E30 or E50, a suitable downpipe and calibration. Gen 1 B58s in particular can reach the limits of the factory HPFP as fuel demand increases, which is why B58TU or aftermarket HPFP upgrades are so common on higher-powered builds.

Once the target moves beyond 600 bhp, the standard turbo becomes the bigger limitation. Hybrid and upgraded turbochargers such as the Pure800 can provide considerably more airflow, but making this level of power reliably requires looking at the car as a complete package. Upgraded fuelling, cooling, intake and exhaust flow, drivetrain condition and a properly developed custom tune all become increasingly important.

It is worth remembering that Stage 1, Stage 2 and Stage 2+ aren't universal specifications. Different tuners use the terms differently, and quoted B58 horsepower figures can vary significantly depending on fuel, dyno type, whether the figure is measured at the wheels or crank, environmental conditions and the exact B58 variant. Treat the figures above as realistic ranges rather than guaranteed outputs.

What are the best B58 mods?

The best B58 mods depend on what you actually want from the car. If it's a fast road car, you don't need to throw the entire aftermarket catalogue at it. A well-chosen intake, exhaust and quality remap can completely change the character of a B58-powered BMW. Start chasing Stage 2, ethanol blends or bigger power figures, though, and upgrades to the exhaust, fuelling and cooling systems become increasingly important.

B58 Intake

A performance intake is one of the easiest ways to add a bit more theatre to the B58. The biggest difference is sound – expect considerably more turbo spool and induction noise – but a less restrictive intake can also improve airflow as power demand increases.

On a standard or Stage 1 car, the factory airbox is already very capable, so an intake shouldn't be viewed as a huge standalone power upgrade. Instead, it's a modification that improves the driving experience while giving the engine more breathing room as you progress further with your build.

When do you need one?
Not essential for Stage 1, but a worthwhile upgrade for sound, improved airflow and higher-powered builds.

B58 Downpipe

The downpipe sits immediately after the turbocharger, making it one of the most important areas of the exhaust system when increasing power. A less restrictive downpipe reduces backpressure and allows exhaust gases to leave the turbo more efficiently, which is why it is commonly paired with Stage 2 software.

There are two main routes: a catless downpipe or a high-flow sports cat. Catless systems offer the least restriction but aren't suitable for UK road use where emissions requirements apply. A quality high-flow sports cat offers a better solution for a road car, improving exhaust flow and sound while retaining a catalytic converter.

When do you need one?
Typically when moving to a Stage 2 calibration that has been specifically designed for an upgraded downpipe. Always match the hardware to the requirements of your chosen tune.

B58 Charge Pipe

Gen 1 B58 engines use a plastic factory charge pipe. It works perfectly well at standard boost levels, but age, repeated heat cycles and increased boost pressure can make the original plastic pipe a potential weak point on a modified car.

Replacing it with an aluminium charge pipe removes that concern and gives you a more robust connection capable of dealing with increased boost. It isn't a modification you should expect to deliver a noticeable power increase on its own; think of it as a supporting reliability upgrade as you start asking more from the engine.

When do you need one?
Worth considering on tuned Gen 1 cars, particularly as boost increases or if the original pipe is showing signs of deterioration.

B58 HPFP Upgrade

As you start chasing more power – particularly when using ethanol-blended fuels – the amount of fuel the engine needs increases significantly. This is where the high-pressure fuel pump, or HPFP, becomes important.

The original Gen 1 B58 fuel pump has less flow capacity than the later B58TU system. One popular upgrade is therefore fitting a B58TU HPFP to a Gen 1 engine, providing additional fuelling headroom without immediately moving to a more extreme fuel system. For higher-power builds, aftermarket pumps from specialists such as Dorch provide substantially greater capacity.

An HPFP upgrade isn't about making power by itself. It gives the fuel system the capacity required to safely support the additional airflow, boost and ethanol content demanded by more aggressive tuning.

When do you need one?
Generally once the standard fuel system becomes the limiting factor, particularly on Gen 1 Stage 2+ setups, ethanol blends or upgraded-turbo builds. Your tuner should determine the fuel system required for your chosen map and power target.

B58 Cooling Upgrades

More boost creates more heat, and controlling that heat becomes increasingly important as you push the B58 harder. The B58 uses a water-to-air charge-cooling system, with a front-mounted heat exchanger helping remove heat from the charge-cooler circuit.

For a lightly modified road car, the standard system is remarkably capable. Cooling upgrades become more valuable when the car is subjected to repeated hard acceleration, track use, hot ambient temperatures or more aggressive tuning. A larger heat exchanger can improve the system's ability to reject heat, helping keep intake temperatures more consistent from one pull to the next.

Upgraded charge-cooler manifolds can take things further on higher-powered builds, increasing cooling capacity and helping manage the additional heat generated as boost and airflow rise.

When do you need one?
Most beneficial for cars driven hard repeatedly, track cars and higher-powered Stage 2+ or upgraded-turbo builds where consistent intake temperatures become increasingly important.

B58 Exhaust

If you want your B58 to actually sound like a turbocharged straight-six, an exhaust is one of the most rewarding modifications you can make. Depending on the system, an axle-back or cat-back exhaust can add considerably more depth and character without fundamentally changing the engine's tune.

The key distinction here is between an exhaust fitted primarily for sound and changes made further upstream to increase exhaust flow for tuning. A cat-back system alone isn't going to transform B58 power output, but combined with the right hardware and software it can form part of a much more complete performance package.

When do you need one?
You don't. And that's precisely why it's such a good modification. If sound and driving experience matter to you, an exhaust can be worthwhile at any stage of a B58 build.

B58 Remap / Software Tuning

If outright performance is the goal, software is where the biggest gains begin. The B58 responds exceptionally well to ECU tuning, with Stage 1 software capable of unlocking significantly more power and torque without requiring major hardware changes.

From there, Stage 2 and more advanced calibrations allow the software to take advantage of supporting modifications such as an upgraded downpipe, fuel pump and, eventually, a larger turbo. The important thing is to build the car around a clear power target rather than fitting parts first and deciding on the tune afterwards.

When do you need one?
Whenever you want to unlock meaningful additional power. Choose your desired power level first, then select the software and supporting hardware needed to achieve it safely.

Recommended Upgrade Paths by Vehicle

Not every B58 build should follow the same pattern. Earlier Gen 1 cars such as the M140i and M240i have different fuelling and hardware supporting requirements to the later M340i, M440i and Toyota's GR Supra models, so the best upgrade path depends on both the car you own and the power you want to achieve.

BMW M140i & M240i – B58 Gen 1

The M140i and M240i remain two of the best starting points for a B58 build. Even in standard form at 335bhp and 386bhp they're seriously quick, and you don't need an extensive list of modifications to make a noticeable difference.

Fast Road / Stage 1 – around 400–440 bhp
Start with a quality Stage 1 remap. The factory hardware is capable of supporting a substantial increase over standard power, while a B58 performance intake can be added for more induction sound and improved airflow. An upgraded exhaust is another worthwhile addition if you want to bring out more of the B58's straight-six soundtrack.

Stage 2 – around 440–480 bhp
Moving to Stage 2 typically means adding a suitable high-flow downpipe alongside the required software. An upgraded charge pipe becomes increasingly worthwhile on Gen 1 cars as boost rises, while a performance intake and exhaust can further improve airflow and sound.

Stage 2+ / 500 bhp territory
This is where the Gen 1 fuel system becomes more important. The original high-pressure fuel pump can become a limiting factor, particularly when using ethanol-blended fuels, so a B58TU HPFP or suitable aftermarket pump is a common upgrade. Pair that with the appropriate downpipe, cooling and custom or Stage 2+ calibration and the M140i/M240i becomes a seriously capable package.

600+ bhp
Beyond this point, you're moving away from simple bolt-on tuning. An upgraded turbo, additional fuelling capacity, improved cooling and a properly developed custom calibration become essential parts of the build. At these power levels, drivetrain, tyres, brakes and chassis setup deserve just as much attention as the engine.

BMW M340i & M440i – B58 Gen 2

The later M340i and M440i start from a stronger position, with the B58TU bringing revised cooling, fuelling and engine hardware. As a result, they can make impressive power without immediately requiring some of the supporting upgrades commonly associated with Gen 1 builds.

Fast Road / Stage 1 – around 420–450 bhp
For most road cars, a Stage 1 calibration is all that's needed to transform the performance. An intake and exhaust can then be added for more induction noise and a stronger exhaust note without turning the car into an overly compromised daily driver. Before buying tuning software, however, remember to check the DME. Later cars may require a DME unlock before the ECU can be remapped., with post-mid-2020 DMEs potentially requiring a specialist unlock solution.

Stage 2 – around 450–500 bhp
A suitable high-flow downpipe and matching Stage 2 software take advantage of the B58TU's additional headroom. Cooling upgrades become worth considering if the car sees repeated hard use, while the later fuel system generally provides more capacity than the original Gen 1 setup.

500–600+ bhp
Once the target moves substantially beyond Stage 2 power, the same principles apply as they do to Gen 1: turbocharger airflow, fuelling and heat management become the priorities. At this point, build the hardware around a defined power target and the requirements of your chosen tuner rather than simply adding parts one at a time.

Toyota GR Supra 3.0

The six-cylinder GR Supra shares its B58 DNA with BMW, which means it responds to many of the same tuning principles. A Stage 1 calibration can deliver a substantial improvement with relatively little hardware, while an intake and exhaust bring out considerably more of the engine's character.

From there, a suitable downpipe and Stage 2 software open the door to further gains, with upgraded cooling, fuelling and eventually a larger turbo becoming relevant as the power target increases.

There is one important caveat with the Supra: the exact B58 specification and ECU security vary by model year and market. Before ordering tuning hardware or software, identify the engine and DME fitted to the car rather than assuming every A90/A91 Supra follows the same upgrade path.

Which B58 upgrade path should you choose?

For a road-driven B58, more power isn't always the answer. A well-sorted Stage 1 M140i or M340i with the right tyres, brakes and chassis upgrades can be a better car to drive than a 600 bhp build that struggles to put its power down.

Start by deciding what you actually want from the car. If it's a quick daily driver, Stage 1 and a few carefully chosen supporting mods may be all you need. If the goal is 500 bhp or more, plan the fuelling, cooling and supporting hardware from the outset. And if you're chasing 600+ bhp, treat it as a complete build rather than simply a turbo upgrade. The B58 gives you plenty of headroom. The trick is building the car around how you actually intend to use it.

B58 Stage 1 vs Stage 2: What's the Difference?

The main difference between B58 Stage 1 and Stage 2 tuning is the supporting hardware required. B58 Stage 1 typically uses an ECU (Engine Control Unit) remap on otherwise standard engine hardware, making it the easiest and most cost-effective route to more power. B58 Stage 2 combines more aggressive software with supporting modifications – most commonly a freer-flowing downpipe – allowing the engine and turbo to produce more power while managing the additional airflow and boost.

For most B58 owners, Stage 1 offers the best balance between performance, cost and everyday usability. Stage 2 takes things further, but requires more investment in hardware and introduces additional considerations around emissions, cooling and fuelling.

*Approximate hardware costs exclude ECU software, labour and any DME unlocking required. Requirements and power figures vary by B58 generation, fuel quality, tuner and vehicle.

Is B58 Stage 1 worth it?

For most road-driven B58s, Stage 1 is the sweet spot. The engine responds exceptionally well to software alone, delivering a noticeable increase in power and particularly mid-range torque without requiring major hardware changes.

That also makes Stage 1 a sensible place to start if you're new to B58 tuning. You can experience a significant performance increase before deciding whether the additional cost and hardware required for Stage 2 are actually worthwhile.

What do you need for B58 Stage 2?

A B58 Stage 2 setup typically combines an ECU remap with a freer-flowing downpipe. Reducing restriction immediately after the turbo allows the calibration to take advantage of improved exhaust flow and target more performance than a conventional Stage 1 setup. A performance intake, exhaust, charge pipe and cooling upgrades can complement a Stage 2 build, but they aren't automatically mandatory simply because the car is labelled "Stage 2". The exact hardware should always be matched to the requirements of the calibration you're running.

For UK road cars, the choice of downpipe also matters. A catless downpipe may offer maximum flow but can create emissions, warning-light and MOT compliance issues. A quality high-flow sports cat is the more appropriate route for a road-focused build where you want improved flow while retaining a catalytic converter.

What about B58 Stage 2+?

Stage 2+ generally takes the B58 beyond the conventional downpipe-and-remap setup by introducing additional fuelling capability. This is particularly relevant on Gen 1 engines, where the original high-pressure fuel pump can become a limiting factor as power and fuel demand increase.

An upgraded B58TU or aftermarket HPFP, suitable calibration and, where appropriate, ethanol-blended fuel can move a B58 towards the 500 bhp mark and beyond. At this stage, cooling, fuel quality and the overall condition of the car become increasingly important.

Ultimately, Stage 1 is the better choice for most daily-driven B58s, offering a significant performance increase for relatively little investment. Stage 2 makes sense if you want to extract more from the standard turbo and are happy to invest in the supporting hardware. Beyond that, you're starting to move into a more serious B58 build where fuelling, cooling and eventually the turbo itself become the limiting factors.

Is the BMW B58 engine reliable?

The BMW B58 engine has built an excellent reputation for reliability, particularly considering the performance and tuning potential it offers. Both Gen 1 and Gen 2 engines have proven capable of covering high mileages when properly maintained, and the core engine itself – including the block, crankshaft and other major internal components – is generally very robust. Gen 2 builds on that foundation with a number of revisions to the cooling, fuelling and engine management systems, while also addressing some of the issues associated with earlier engines.

That doesn't mean the B58 is without its problems. As these engines get older, there are several known weak points worth watching – particularly if the car has been modified or driven hard.

Oil filter problems

One slightly unusual B58 issue is the oil filter breaking apart or becoming stuck in the housing during removal. In some cases, part of the filter can remain behind when it is removed, making an otherwise routine oil change considerably more complicated.

Using a quality OE or OEM-specification oil filter, changing the oil regularly and taking care when removing the old filter can help reduce the risk. If a filter does break up, make sure all of the old material is removed rather than simply installing a new filter on top of it.

The oil filter housing itself is another area to monitor as B58s accumulate mileage. Its plastic construction and seals are subjected to repeated heat cycles, and leaks can develop over time. Coolant or oil loss around the housing should therefore be investigated rather than simply topped up and ignored.

PCV valve failure

PCV (Positive Crankcase Ventilation) problems are particularly associated with Gen 1 B58 engines. The system uses a diaphragm integrated into the valve cover, which can split or fail with age.

Typical symptoms include a high-pitched whistling noise from the engine bay, increased oil consumption and blue or white smoke from the exhaust. Because these symptoms can easily be mistaken for something more serious, the PCV system is a sensible first area to investigate if an otherwise healthy Gen 1 B58 suddenly starts smoking.

The problem appears to be less prevalent on later B58TU/Gen 2 engines, but the crankcase ventilation system is still worth monitoring as mileage increases.

Coolant loss and leaks

Cooling-system health is particularly important on the B58, and unexplained coolant loss should never simply be accepted as normal. Potential leak points include the water pump, expansion tank and cap, hoses and connections, oil filter housing and other plastic cooling-system components.

The expansion tank cap is a particularly simple item to overlook. If it no longer maintains the correct system pressure, coolant can escape without leaving the sort of obvious leak you might expect. If a B58 regularly needs coolant topping up, the system should be inspected and pressure tested to establish where it is going.

Later B58TU engines use a more sophisticated split-cooling and thermal-management system. It improves temperature control and efficiency, but also introduces additional components that can potentially develop leaks or faults as the engine ages.

Valve cover and gasket leaks

Like many modern BMW engines, the B58 uses a plastic valve cover with rubber sealing gaskets. Repeated heat cycles can eventually cause the gasket to harden and leak, while the plastic cover itself can also deteriorate with age.

Look for oil around the top of the engine, oil collecting around the spark plug area, a burning-oil smell or visible signs of leakage around the valve cover. These issues become more relevant as cars reach higher mileages, so they are worth checking during routine servicing.

How to keep a B58 reliable

Good maintenance becomes even more important once you start tuning a B58. More boost and power place greater demands on the oil, cooling, ignition and fuel systems, so preventative maintenance should come before performance upgrades.

For a healthy B58, we'd concentrate on a few fundamentals:

• Change the engine oil and filter regularly. Use the correct BMW-approved oil specification and a quality filter rather than stretching service intervals on a tuned or regularly hard-driven car.
• Keep an eye on coolant levels. A small change once isn't necessarily cause for alarm, but repeated coolant loss needs investigating.
• Inspect the cooling system for leaks. Look around the expansion tank and cap, water pump, oil filter housing, hoses and connections for dried coolant residue or signs of seepage.
• Watch for PCV symptoms. Whistling, unexplained smoke or increasing oil consumption can point towards a failing PCV system, particularly on Gen 1.
• Check for oil leaks. The valve cover and oil filter housing are sensible areas to inspect as mileage increases.
• Stay on top of spark plugs and ignition components. This becomes particularly important on remapped cars running increased boost, where worn plugs or coils can quickly reveal themselves as misfires under load.
• Warm the engine properly before driving it hard. Allow the oil and coolant to reach operating temperature before repeatedly using full boost.
• Maintain the car for its level of tune. A 500 bhp B58 driven hard requires more attention than a completely standard road car. Shorter servicing intervals and more frequent checks become sensible as power and usage increase.

The key takeaway is that the B58's reputation for reliability is well deserved, but it shouldn't be confused with being maintenance-free. Gen 1 cars are now old enough that age-related seals, plastics and cooling components deserve attention, while later Gen 2 engines benefit from BMW's revisions but still need proper servicing. Look after the fundamentals and the B58 remains an exceptionally strong base for both a dependable daily driver and a seriously quick modified BMW.

B58 vs N55

The N55 set the foundations for BMW's modern turbocharged straight-six engines, but the arrival of the B58 in 2015 represented a significant step forward. Both are 3.0-litre turbocharged straight-sixes using direct injection, a single twin-scroll turbocharger, Double-VANOS and Valvetronic, but the B58 was designed to deliver greater performance, efficiency and durability while forming part of BMW's newer modular engine range.

One of the biggest differences is the engine block. The N55 uses an open-deck design, while the B58 moved to a stronger closed-deck construction, providing greater rigidity and cylinder support as boost and cylinder pressures increase. BMW also increased displacement slightly from 2,979cc in the N55 to 2,998cc in the B58, while the original B58 used a higher 11.0:1 compression ratio compared with 10.2:1 for the N55.

The difference was immediately apparent when the B58 replaced the N55 in the 3 Series. The N55-powered 335i produced 306hp and 400Nm in UK specification, while the B58-powered 340i increased this to 326hp and 450Nm. But outright factory power was only part of the improvement.

For enthusiasts, it's the B58's strength and tuning potential that really separates the two. The N55 remains a very capable tuning platform, but its open-deck block and supporting systems can become greater considerations as power rises. The B58's stronger closed-deck construction, improved charge cooling and revised turbo and fuelling systems give tuners considerably more headroom to work with.

The B58 didn't reinvent BMW's turbocharged straight-six formula – it refined it. It took much of what enthusiasts already loved about the N55 and added a stronger foundation, improved thermal management and greater tuning potential. That combination is a major reason the BMW B58 engine has gone on to become one of the most highly regarded engines in the modern BMW tuning scene.