The BMW S52 is an engine that has historically caught a lot of flack. The main reason is that there is an arguably superior version of it out there. The S52 is the straight-6 DOHC M-variant engine found in US and Canadian-spec E36 M3s and Z3Ms. While the S52 lacks some of the tech found on the Euro-spec S50 engine, the S52 is a fantastic engine in its own right.
The S52 is, in most basic terms, a bored and stroked M52 engine. The M52 was BMW’s replacement for the widely loved M50 engine that preceded it. The M52 and S52 are both known for their unparalleled strength and reliability, sharing a cast-iron block and aluminum head construction. While the M52 and S52 are clearly blood relatives, the S52 features some additional characteristics that make it worthy of being placed in one of the best-performance BMWs of all time.
In this article, we’ll discuss the BMW S52 engine, including its build and construction, similarities and differences with the Euro S50 engine, some of the S52’s most common issues, and some common performance modifications.
BMW S52 Engine Specifications
Engine: BMW S52
Engine Configuration: Inline-6 Cylinder
Displacement: 3,152 cc (192 cu in)
Aspiration: Naturally Aspirated
Valvetrain: DOHC W/ Single VANOS
Block/Head Material: Cast Iron/Aluminum
Bore x Stroke: 86.4 mm x 89.6 mm
Compression Ratio: 10.5:1
Weight: Long Block ≈ 330lbs
Horsepower: 240 hp @ 6,000 rpm
Torque (lb-ft): 236 lb-ft @ 3,800 rpm
BMW S52 Engine Applications
- 1996-1999 E36 M3 (Canada and United States only)
- 1998-2000 E36/7/8 Z3M (Canada and United States only)
BMW S52 Engine vs S50 Engine
There is a lot to cover as far as the differences between US-spec S52 engines and Euro-S50 engines are concerned. It is important to understand that there are multiple variants of the S50 as well. In total, there are three: the S50B30US, S50B30 (Euro), and S50B32 (Euro). To make it a little bit more confusing, the US actually did receive the S50 in S50B30US form. Let’s break down these three engines first before comparing them to the S52.
The S50 that the US received was quite underwhelming when compared to the European versions. Since the Euro S50 was expensive to manufacture and didn’t meet US emissions regulations, BMW chose not to use it in American M3s. Instead, they chose to refine the existing M50 engine found in lower trim E36 models. The “S50US,” as it is colloquially called, features stepped VANOS only on the intake side, is slightly more restricted in terms of gas flow, and lacks individual throttle bodies.
BMW S50B30 (Euro)
Unlike the US-spec S50B30US, the Euro S50B30 is in an entirely different league. The Euro S50 was still based on the M50 engine architecture but was revised massively. In comparison to the M50, the S50 has a wider bore, longer stroke, and an elevated compression ratio at 10.8:1. The B30 features single VANOS variable valve timing on the intake cam, but it is infinitely variable as opposed to the stepped version found on the S50US. The Euro S50B30 also features signature individual throttle bodies, characteristic of most high-performance M-engines. ITBs, as they are commonly called, helped the S50B30 achieve higher top-end performance.
The S50B32 is the engine most commonly compared to the S52B32 due to their shared displacement. Both the S50B32 and S52B32 are 3.2L engines. The S50B32 was introduced for the 1995 model year, and had several performance benefits over the B30. With the displacement bump over the S50B30, the S50B32 also received dual-VANOS on both intake and exhaust cams, a secondary oil pump, and the redline was increased to 7,600 rpm. The change in stroke and bore also caused the compression ratio of the S50B32 to increase to 11.3:1.
While the S50 engine is based on the M50, the S52 engine is based on the newer M52 platform that succeeded the M50. For that reason, the S52 has a lot more in common with the M52 than it does the S50. As we stated earlier, the S52 is essentially a bored and stroked M52 with some additional internal changes. Like the S50US, the S52 features 2-step VANOS on only the intake side. Other than that, the S50 and S52 both use cast iron blocks and aluminum cylinder heads.
If we look at the S50B32 and S52B32 specifically, it is much easier to point out the differences than the similarities. The S50 head has much bigger intake and exhaust ports and bigger intake and exhaust valves, fed through 6x50mm butterflies and released through a tuned length exhaust manifold. The S50B32 features dual-VANOS on both the intake and exhaust sides, which is infinitely variable, compared to the S52’s two-step intake-only VANOS.
Additionally, the S50 features larger cams (for dual VANOS), a higher redline (7,600 rpm vs 6,500 rpm), a larger 3.5” MAF, bigger injectors, and a more sophisticated engine management system. The S50 also uses individual throttle bodies while the S52 does not.
On paper, it doesn’t look like the S52 has a lot going for it when compared side-by-side with its snobby European cousin. However, perspective is everything. If anything, the comparison should show that the S50B32 is a masterpiece of an engine, and the S52 is a great one.
Stock BMW S52 Engine Performance
While the S52 might be less powerful than the S50, it still puts out an impressive 241 horsepower and 263 lb-ft of torque. Low-end torque might be the most standout feature of the S52, as it produces peak torque at just 3,800 rpm. Most of BMW’s naturally aspirated inline-6 engines are known for their extremely linear powerband and the S52 is no exception. It delivers power very smoothly and evenly all the way up to 6,500 rpm.
While the S52 is often said to be just a souped-up M52, there are some important distinctions that make the S52 far superior. Obviously, the most significant advantage is the S52’s 0.4L of extra displacement over the M52B28. That accounts for most of the 50 horsepower discrepancy. In addition, the S52 has more aggressive, and lighter, cams than the M52, which directly translates to more top-end power. It also has upgraded valve springs and a less restrictive exhaust from the factory.
While the S52’s stock performance might be mediocre by today’s standards, the E36 M3 wasn’t a slouch back in the day. It would be hard to consider it one today. The S52 redeems itself in reliability and modifiability where it might lack in off-the-shelf power. Its cast-iron bottom end makes it an extremely strong and dependable engine that is also highly receptive to modification.
BMW S52 Engine Upgrades
The S52 is nearly 30 years old at this point and, as a result, has been tinkered with endlessly by now. As with most BMW engines, the S52 has a very wide breadth of mods available for it, ranging from simple bolt-ons to forced-induction kits. The S52 is truly endlessly modifiable, so the right upgrades for you really depend on what your budget and power goals are.
For those looking for performance similar to what a Euro S50 offers, some simple bolt-on mods will get you in the ballpark. You likely won’t even need to crack open the valve cover to boost horsepower by a good amount. For the sake of this guide, we’ll primarily focus on cost-effective bolt-ons that will yield the best results.
With that being said, forced induction is really the primary way to truly pump sizable horsepower figures out of an S52. The S52 is already a very efficient engine from the factory. BMW did a very good job of truly optimizing its performance. There are a ton of great plug-and-play F/I kits available for the S52, including both supercharger and turbocharger kits.
1) S52/M50 OBD1 Intake Manifold Swap
While the M52, and S52 as a result, is arguably a better engine than the M50 that preceded it, the M50 did do a couple of things better. One of the most significant advantages of the M50 was its superior intake manifold. Overall, the M50’s intake manifold flows around 40% better on each cylinder than the M52 and S52 manifold. The M50’s intake manifold has a much simpler design with long and wider runners and a shared plenum with the throttle body in the middle.
In addition to being the better flowing manifold, the M50 manifold is also less prone to failure. The stock S52 manifold is known to leak from a variety of places such as the intake hoses, DISA diaphragm, the ICV rubber fitting, and vacuum hoses on the back. The smaller M50 manifold also clears up quite a bit of room in the engine bay compared to the bulky design of the stock S52 manifold.
The overall process to swap manifolds is somewhat involved, but can generally be done in a couple of hours if you know your way around a socket wrench. Some additional adapters and modifications will be required to make everything work correctly. You’ll need to match the S52 and M50 ports using an adapter, modify the S52 fuel rail, modify the idle control valve, intake air temp sensor, and VANOS solenoid connector among other things. For a full instructional write-up, check out this article by seemslegitgarage.com.
S52 Engine / M50 Intake Manifold Swap Performance Gains
In terms of the overall effect, the intake manifold swap can boost S52 performance anywhere between 15 and 50 horsepower depending on other considerations like existing mods and engine tune. Typically, horsepower gains from this swap scale with other performance mods. It is especially effective when paired with forced induction.
Most S52 owners that have performed the swap claim that there is a slight horsepower decrease at low rpms if you do the swap without an accompanying tune. However, even without a tune the high rpm performance will be significantly increased. With a tune, you won’t lose any low rpm power and high rpm performance will be increased even more substantially.
2) S52 Engine Cold Air Intake
A performance intake is an excellent option for those looking for a relatively inexpensive S52 performance modification. Depending on how you look at it, a performance intake can be considered a great starting point or the finishing touch to a highly tuned build. The purpose of an upgraded performance intake is to increase engine breathability over the stock setup. In general, the performance of an upgraded intake scales with engine performance, as highly modified engines can often be throttled by poor airflow.
In addition to marginally increasing horsepower and torque, there is the potential that an S52 intake upgrade will slightly improve throttle response. Depending on the construction of the upgraded intake, the inertia and flow characteristics of the incoming air can change the engine performance. While an upgraded intake doesn’t inherently increase throttle response, it can be a consequence of the modified airflow characteristics.
While cold air intakes typically improve horsepower and torque more on turbocharged/supercharged cars, they can provide a moderate 5-10 hp and 5-10 lb-ft increase on N/A engines as well. Both Dinan and aFe provide solid cold air intake options for the S52 which will be linked below.
Dinan Performance Cold Air Intake:
Purchase Here: Dinancars.com
aFe S52 Performance Cold Air Intake:
Purchase Here: Turnermotorsport.com
3) S52 Engine Exhaust Upgrade
Cat-back exhausts are without question the most common type of exhaust fitted to lightly modified E36 M3s and Z3Ms. Cat-back exhausts are exactly what they sound like. They replace all of the factory exhaust components from the catalytic converter to the exhaust tip. This type of exhaust is generally made of stainless steel and is made to improve exhaust gas flow out of the engine, resulting in a bit more power and a lot more noise. Typically, a quality high-flow exhaust system can increase power by around 10-20 horsepower and 15-25 lb-ft of torque.
Aftermarket cat-back systems can vary a good amount in terms of their pipe diameter, tip diameter, and how they exit the vehicle. Aftermarket exhausts tend to also be lighter than the factory S52 exhaust, which improves performance and increases fuel economy. The sound produced by an aftermarket E36 M3 / Z3M exhaust is heavily dependent on the diameter of the exhaust piping and the type of muffler that it employs. Our top S52 exhaust picks are as follows:
BimmerWorld Magnaflow E36 M3 Cat-back Exhaust:
Purchase Here: Bimmerworld.com
Eisenmann E36 M3 Performance Exhaust :
Purchase Here: Eisenmann.com
BMW S52 Engine Reliability
In terms of reliability, the S52 is widely known as one of the most, if not the most, reliable M engines to date. As the S52 shares the same cast-iron block as the also notoriously-reliable M52, they can last well beyond the 200,000-mile mark with proper care and maintenance. The S52’s simplicity and high-quality build materials are what truly make it bulletproof if looked after diligently.
As with any engine, the S52 is prone to a few issues, especially at higher mileages. Similar to most other BMW engines, S52s are reliant on up-to-date maintenance and servicing. If you stay on top of maintenance, an S52 will rarely ever let you down. Here are the most common issues that S52 owners report:
- VANOS Unit Failure
- Cooling System Issues or Leaks
- Power Steering Leaks
1) S52 Engine VANOS Unit Failure
VANOS is BMW’s version of variable valve timing and has been around since the early 90s. The S52 has a single VANOS system, on the intake camshaft only, which uses oil pressure to adjust the cam phase, controlling the advance and retardation of the intake valves. While a good system, VANOS is known to be problematic at high mileage. That is pretty much the case for any BMW engine that has VANOS, including the S52.
Typically, the S52’s VANOS system will fail in one of two ways. Either the internal solenoid will fail due to age and wear, or the internal O-ring seals will fail. Both of these VANOS failures will produce similar symptoms including the following:
- Loss of overall torque and power, especially under 3,000 rpm
- Bogging then surging at 3,000 rpm
- Loud idle and intermittent idle issues
- Difficulty starting or difficulty setting off from a stop
- Increased fuel consumption
- VANOS engine fault codes
In general, the only solution for this issue is to replace the VANOS unit with a refurbished one or send your failing unit to a shop or technician who is able to rebuild it. Unfortunately, this is often a pretty expensive repair. The complexity of the VANOS system combined with the need for specialty tools makes a VANOS repair a difficult one to DIY. With that being said, it is possible. If you are interested in attempting a repair yourself, check out this VANOS Repair Guide.
We also recommend checking out Dr. VANOS, a BMW repair shop located in Texas, that specializes in VANOS rebuilds and repairs.
2) S52 Radiator and Expansion Tank Leaks
The cooling system on the S52 seems to be the Achilles heel of many E36 M3s. The majority of radiator support parts are made of plastic on these cars, which means they are very prone to cracking and leaking. Radiator leaks are common and usually stem from the top radiator pipe and the thermostat housing.
Additionally, the coolant expansion tank is also made of plastic and is prone to cracking and leaking.
S52 Engine Coolant Leak Symptoms
- Coolant fluid on your garage floor
- Frequent engine overheating
- Low coolant light on the dash
If you are experiencing common overheating, you either have a failed/cracked radiator, or a leak somewhere in the cooling system. If your engine is overheating, pull over and have it towed to a shop! Continuing to drive on an overheated engine can result in warping the head or internals, requiring a full engine replacement.
3) S52 Engine Power Steering Leaks
Power steering leaks are another very common problem with 90s BMW engines including the M50, M52, and S52. Due to the fact that they are reliant on rubber hoses, aging hose clamps, and plastic reservoirs, the S52’s power steering system is another point of failure at high mileage. Even if your M3 or Z3M doesn’t have too many miles on the odometer, age tends to make power steering hoses brittle and prone to leaks.
Some common leak points include the following:
- Power steering return hose
- Failing return hose clamp
- Power steering reservoir cap / gasket
- Brittle or cracked hoses
Luckily, most of the time power steering leaks arise from a cracked rubber hose somewhere near the power steering reservoir. If that is the case, the repair can be done very cheaply and easily, as power steering hoses typically only run around $20 and can be replaced with just a flathead screwdriver or 8mm socket.
The easiest way to check for the source of a power steering leak is to park your car and wipe down any previously wet areas with a shop towel. Make sure to also dry the ground under the car as well. Once all of the hoses and areas around the power steering reservoir are dry, start the car. If any of the previously dry areas become visually wet, that is a source of a leak.
BMW S52 Engine Summary
Despite being overshadowed by its European counterpart, the S52 is one of the pillar engines in BMW’s performance straight-6 catalog. While it lacks dual-VANOS, ITBs and other tech featured on the S50B30, the S52 is still a very efficient and reliable engine.
The S52 still puts out an impressive 240 horsepower and 236 lb-ft of torque with 3.2L of displacement. While that might not be anywhere near as competitive as the power that modern M-cars are producing, those numbers are still respectable. If you aren’t satisfied with the S52’s stock power production, there’s a lot that you can do about it. The S52 has a ton of aftermarket support, ranging from simple bolt-ons to forced induction kits. An M50 intake manifold swap, cold air intake, and exhaust will see a significant bump in horsepower and torque that will truly liven up an E36 M3 or Z3M.
Beyond being highly modifiable, the S52 is widely known in the BMW community as being one of the most bulletproof 6-cylinders that BMW has ever produced. That boils down to its high-quality production materials, including a cast-iron block and aluminum cylinder head, and its overall simplicity. The most common, and unfortunately most expensive, problem that plagues many high mileage S52s is a failing VANOS system. Luckily, there are plenty of BMW shops out there that can perform a VANOS repair for cheaper than what BMW would charge at a dealership.
If you enjoyed this article and are interested in other vintage BMW content, check out our BMW E30 Engine Swap Guide. As always, safe driving!