Ultimate BMW M50 Engine Guide

The BMW M50 engine is one of the brand’s first modern inline-six engines utilizing 21st-century engine technology. Compared to other BMW inline-six engines of the past, like the M20, the M50 was not only technically advanced for the time, but also reliable, capable, and easy to work on. It was also featured in some of the most iconic BMW models from the 90s, including the E36 3-Series and E34 5-Series. As a result, the M50 truly became the blueprint for BMW’s inline-six engines for decades to come, also cementing the formula as BMW’s bread and butter.

In this guide, we’ll take a look at the M50 inline 6 and how it stacks up to other engines that BMW produced after it. We’ll also cover general engine specs, design basics, the best performance upgrades, common problems, and everything else that you need to know about the BMW M50 engine. 

Engine Specs

Design Basics

Compared to some other engines running concurrently with the M50 at the time, the 2.0/2.5L inline 6 wasn’t around for very long. In fact, its production run only lasted only six years between 1990 and 1996. During its stint, it was used in BMW’s 90s flagship models, including the E36 3-Series and E34 5-Series. 

Prior to the M50, BMW had already established themselves as a formidable engine manufacturer, especially when it came to inline-six-cylinder engines. The M20 inline-six engine that preceded the M50 was reliable and suited its purpose well, but was antiquated by the 90s. The M50 updated the formula to a more 21st-century approach, utilizing a dual overhead cam, four-valve-per-cylinder top end. It also featured coil-on-plug ignition, in addition to a knock sensor. It also used lightweight materials where it could, including a high-flow plastic intake manifold and an aluminum alloy cylinder head.

The M50 was offered in three different displacements, including 2.0L, 2.4L, and 2.5L variants. The United States only received the 2.5L M50B25 and M50B25TU variants of the M50 (barring the M3-exclusive S50B30US engine) as the rest were only sold in other markets.

Only two years after the M50’s release, it received an overhaul. In BMW terminology, these updated engines are referred to as “Technical Update” or “TU” engines. As a result of the technical update, the M50TU received variable valve timing on the intake side of the engine, known as single-VANOS. The M50TU engines were the first BMW engines to use the now famous BMW VANOS variable valve timing system.

Variants and Technical Update

The BMW M50 was offered in three different displacements, including a 2.0L variant, 2.4L variant (in Oceania markets), and a 2.5L variant. If you live in the US, you’ve likely only seen the M50B25 and M50B25TU variants of the engine, as those are the only variants that we received stateside. In addition to being offered in three different displacements, the M50 also received a technical update in 1992, introducing the TU models to the M50 lineup. 

The 1992 update brought single-VANOS to the intake side of the engine, making the M50 the first BMW engine to use variable valve timing. The introduction of single VANOS also changed the characteristics of the engine completely, marginally improving torque numbers, lowering the peak torque threshold, and allowing for higher compression ratios. Despite the upgrade to intake cam variable valve timing, the TU engines made the same power as the non-TU engines.

Here are the variants of the BMW M50 and the vehicles that used the engine:

M50B20

The M50B20 is a 2.0L variant of the M50 with a bore and stroke of 80mm x 66mm and a 10.5:1 compression ratio. It produced ​​148 hp at 6,000 rpm and 140 lb-ft of torque at 4,700 rpm.

• 1991-1995 E36 320i
• 1990-1992 E34 520i

M50B20TU

The M50B20TU is the technically updated version of the 2.0L M50B20. It retained a bore and stroke of 80mm x 66mm, but had a higher 11.0:1 compression ratio. It produced ​​148 hp at 5,900 rpm, while peak torque of 140 lb-ft was now available at 4,200 rpm. 

• 1992-1994 E36 320i
• 1992-1996 E34 520i

M50B24TU

The M50B24TU is a 2.4L variant of the M50 with a bore and stroke of 84mm x 72mm and a 10.5:1 compression ratio. Interestingly, there was no pre-TU version of the M50B24TU, making it one of the only BMW engines to have only a TU version. The M50B24TU was used for models exclusively in Thailand and Oceania markets. It produced ​​185 hp at 5,900 rpm and 177 lb-ft of torque at 4,200 rpm.

• 1993-1995 E36 325iA/2.4
• 1992-1996 E34 525iA/2.4

M50B25

The M50B25 is a 2.5L variant of the M50 with a bore and stroke of 84mm x 75mm and a 10.0:1 compression ratio. It produced ​​189 hp at 6,000 rpm and 181 lb-ft of torque at 4,700 rpm.

• 1991-1992 E36 325i, 325is
• 1990-1992 E34 525i, 525ix

M50B25TU

The M50B25TU is the technically updated version of the 2.5L M50B25. It retained a bore and stroke of 84mm x 75mm, but had a higher 10.5:1 compression ratio. It produced ​​189 hp at 5,900 rpm and 184 lb-ft of torque at 4,200 rpm.

• 1993-1995 E36 325i, 325is
• 1992-1996 E34 525i, 525ix

BMW M50 vs M52 Engine

While there is no doubt that the M50 and M52 engines are close siblings, there are a few notable design differences that make a big difference in the overall drivability of both engines. The most obvious difference between the BMW M50 and BMW M52 engines is the discrepancy in displacement in their highest trim. While the M50 (excluding the S50) maxed out at 2.5L with the M50B25, the M52 engine’s top trim (excluding the S52) is 2.8L with the M52B28.

The difference in displacement and presence of dual VANOS M52TUs accounts for the increased torque over the M50B25. Despite the difference in displacement, many BMW enthusiasts claim that pre-TU M52 engines feel very similar to M50TU engines with single VANOS. 

Adding to the engine characteristic differences a bit more, engine geometry comes into play here as well. Due to the fact that the M52B28 is a square engine, meaning that its stroke and bore are the same lengths, it has more desirable power delivery characteristics than the M50B25 which is an oversquare engine. In general, the M52 has a more predictable and even torque delivery, while the M50 wakes up a bit more beyond 3,500 rpm. 

Another significant difference between the two is the M50’s use of OBDI in contrast to the M52’s use of OBDII onboard diagnostics. This plays a role in both aftermarket support and ease of tuning, as many people prefer the M50 over the M52 because there is more support for OBDI-equipped cars which are also subsequently easier to tune. 

While the US-spec M52 with the cast iron block weighs marginally more than the M50, the difference is negligible. On the other hand, M52s with an aluminum block from outside of North American markets weighed around 40 pounds less than the previous generation M50 engine. 

Stock BMW M50 Engine Performance

The M50 truly established the BMW inline-six’s reputation for smooth and predictable power delivery. It is unquestionably the feature that made the M50 such an impactful and well-loved engine. Having owned an M50B25-powered E34 525i, I got so accustomed to the silky power delivery from the M50 that stepping into a modern turbocharged BMW felt choppy by comparison. Just take a look at this dyno for a lightly modified M50-powered E36:

It is nearly impossible to have a more consistent and linear power and torque curve than the one that the M50 produces. Horsepower very steadily grows from 30 to 110 mph (not sure why the dyno doesn’t track RPM) with performance predictably increasing higher in the rev range. If the dyno was for an M50 and not an M50TU, you’d see a nearly flat torque curve across the rev range as well, which brings me to a major difference between the M50 and M50TU in terms of stock performance.

Since the M50TU has single VANOS, it has slightly different torque delivery characteristics than the non-VANOS M50. While the non-VANOS M50 has a very predictable and flat torque curve, the M50TU spices things up a bit when VANOS engages around 4,700 rpm, which is also around 1,300 rpm before the NV M50 reaches peak torque. Most enthusiasts, including myself, like the noticeable bump in torque in the middle of the rev range.

BMW M50 Engine Mods and Upgrades

Despite being a very popular engine in the BMW community, the M50 isn’t the best engine in BMW’s catalog as far as aftermarket performance is concerned. Unless you’re willing to fork out some cash, that is. A large reason for this is the fact that the M50 is already well-optimized from the factory. If you plan on staying naturally aspirated, any big power mods, like cams, increased bore, or individual throttle bodies, are extremely expensive and difficult to achieve.

Forced induction is unquestionably the best option if you are trying to make big power from an M50. For that reason, turbo kits are one of the most popular aftermarket modifications for any M50-powered BMW, especially since the M50 takes boost so well. Going the turbo route isn’t cheap, but it is much easier on the M50 compared to later OBDII engines due to its simplicity.

Most of the more cost-effective and simple modifications available for the M50 won’t net a ton of horsepower but will make the engine more enjoyable to live with.

Performance Chip Upgrade

Of all of the simple bolt-on modifications that you can do to a BMW M50, performance chips yield the best gains overall. With that being said, the gains still aren’t much to write home about. With some options, like the Turner Conforti or the Miller Performance W.A.R. chip, you can expect to gain somewhere in the ballpark of 15-20 horsepower and 10-15 lb-ft of torque. While that isn’t a massive gain, it’s the best that you’re going to do for a little over $200. Ultimately, a performance chip will gain back some of the power that the engine has lost over the years.

Outside of the moderate power and torque gains, there are some other benefits to M50 performance chips too. By remapping ECU parameters, performance chips change the effective power and torque bands of the M50. In the case of the Turner chip, the power curve is moved left, meaning that peak power is made earlier in the rev range than the stock tune. The Turner chip also increases the rev limiter to 7,000 and removes the speed governor, allowing for some extra debauchery.

S52 Cams

One of the best N/A performance modifications that you can do to an M50 is installing cams from an S50/S52. The S50/S52 was found in European/US-spec E36 M3s, Z3M Coupes, and Z3M Roadsters and features more aggressive cam profiles. The S50/S52 cams feature significantly longer duration and higher lift than the factory M50 cams which not only changes the power and torque curves of the engine but also increases both power and torque. While low-end torque generally suffers a bit, high RPM performance sees a dramatic increase with this setup.

The best news is that S50/S52 cams are a direct replacement for the factory M50 cams. It is important to mention that while S50 cams will fit into an M50 using the stock cam trays, you do need to source S52 cam trays in addition to the cams if you go with an S52 set. Other than that, it is a relatively simple modification for the power gains. If you are planning on doing this swap, it is a good idea to refresh your valvetrain components, including lifters, valve springs, and retainers, as the factory components are likely worn and the new cams are more aggressive.

It is also critical to get a tune that can take advantage of the new cams to the fullest. Most M50 performance chips, like the ones that we just covered, should work very well for this purpose. Between the upgraded cams and chip, it is reasonable to expect around 20-30 additional horsepower.

Turbocharger Kit

While expensive, there’s no question that a quality turbo kit is the best bang-for-buck modification for any M50-powered BMW. It is very well known in the classic BMW community that the M50 is one of the best BMW engines of all time to turbocharge. They are incredibly strong from the factory and the block/factory rotating assembly can typically hold up to around 400-500 horsepower with just head studs and a cut-ring head gasket. The M50’s simplicity also makes it a fan favorite to boost, as its OBDI EMS makes tuning for boost possible and easy. Supporting modifications are obviously a big part of the equation, with fueling modifications also being crucial.

Since the M50 is so popular in the aftermarket forced induction community, there are a ton of quality turbo kits available. Obviously, building a custom kit is also an option but requires quite a bit of research and sourcing to put together. Most premade M50 turbo kits range between $3,000-$8,000. While they are expensive, they can add anywhere between 100-500 horsepower on top of the M50’s factory output.

If you are interested in learning more about M50 turbo kits, we wrote an entire article about the subject. Take a look at our BMW E36 Turbo Kit Guide for more information. 

BMW M50 Engine Problems

The BMW M50 is widely considered to be one of the most reliable modern BMW engines, period. That is especially true of the pre-TU engines that lack VANOS. The M50 is a relatively simple, yet modern, engine, making it reliable and easy to repair. In fact, it is so reliable that I put it on my Most Reliable BMW Engines of All Time list. As long as you stay on top of regular maintenance, it is common to see M50 engines with over 300,000 miles on the odometer. Overall, the M50 only has a few serious problems of note, most of them revolving around the cooling system.

• Radiator & Thermostat Failure
• Cracked Expansion Tank & Coolant Leaks
• Water Pump Failure
• Bad Ignition Coils and Spark Plugs
• Rough Idle from Faulty Idle Control Valve or TPS

The cooling system tends to be the common weakness on all M50 engines, with frequent failures across the radiator, water pump, thermostat, and coolant expansion tank. Theoretically, there is nothing wrong with the design or make-up of the cooling system that causes it to fail, these symptoms simply fail over time due to age and normal wear and tear. The one exception to this is the water pump, which does have a common failure point.

On the M50, common failure points are the radiator itself, radiator hoses, the water pump, and the thermostat. Additionally, the coolant expansion tank cracks frequently. All of those issues are caused by time and heat cycles that wear down the components. 

If you are looking for more in-depth information about issues with the M50 engine, take a look at our dedicated BMW M50 Common Problems and Reliability Issues guide. 

The M50 is Undoubtedly One Of BMW’s Most Important Engines

The BMW M50 took over as the mainstay inline-6 powerplant for the majority of BMW’s smaller vehicles including the E36 3-Series and E34 5-Series in the 1990s. In terms of engine technology, the M50 was a seismic leap forward over previous BMW SOHC engines. The M50 introduced a dual overhead cam, 4 valves per cylinder architecture to BMW’s already famous inline-6 recipe, prepping their engine design for the 21st century. 

Only two years into the M50’s build cycle, the M50TU was released, introducing one of the most important modern innovations that would carry all the way to the modern day; VANOS variable valve timing. In addition to newer methods of engine management, ignition technology, and material advancements, the M50 is an engine full of firsts for the brand, truly establishing a formula for BMW to follow for decades.

On top of the M50’s innovations, it is an extremely reliable, versatile, and modifiable engine. The M50 has very few inherent design flaws, with most of its common problems arising due to age and improper maintenance. If taken care of, an M50 can live well beyond 300,000 miles. It is also a very sturdy engine, making it a popular engine to modify, especially with forced induction.

Without the M50, who knows if BMW would even be known and celebrated for their inline-six engines. It truly is one of the most important engines in BMW’s catalog.