June 25, 2024

Distinguishing Between BMW N51 and N52 Engines: Key Differences to Highlight

Among BMW’s inline engine lineup, one name always stands out for reliability: the BMW N52. Another variant of the same engine is the N51, which was introduced for a specific purpose.

Both the N51 and N52 engines represent BMW’s commitment to performance and reliability. Visually, they are indistinguishable, with the only difference being found on the emissions label. Therefore, if you are considering tuning your car, it is crucial to know your exact engine type.

Let’s explore the distinctions between the BMW N51 vs N52 in this article.

Brief History of N51 and N52 Engines

The N52 is a naturally aspirated engine that succeeded the popular M54 from 2004-2015 and was utilized in various BMW models. The N52 became one of the most popular and reliable inline-six engines ever created, followed by its sibling, the N51.

The N51 is nearly identical to the N52, as they were both used in the same cars during the same time period and produced the same power output. The N51 is a slightly modified variant that BMW sold in certain parts of the U.S. to comply with enforced SULEV (Super Ultra Low Emission Vehicle) regulations.

The N51 was essentially developed to offer a more environmentally friendly version of the N52 engine while maintaining the same power output.

Difference Between BMW N51 & N52

  • Both the N51 and N52 engines are originally the same, with some modifications that are only discernible by checking the emissions label on the hood. The N51 engine will display “SULEV,” while the N52 engine will display “ULEV.” More details about SULEV & ULEV will be discussed later on.
  • The N51 is equipped with a “Prem-air” coating radiator that includes an integrated EAC (Environmental Air Catalyst) sensor in the radiator fins to assess radiator functionality.
  • The N51 features a three-stage variable-length intake manifold, whereas the N52 is equipped with a stage-one intake manifold.
  • The N51 has a lower compression ratio of 10.0:1, while the N52 has a compression ratio of 10.7:1.
  • The N51 also has different cylinder head and optimized combustion chamber designs compared to the N52.
  • Furthermore, the cylinder head cover and crankcase ventilation systems differ between the two engines.
  • The N51 includes an Airbox with an Activated carbon filter for EVAP control.
  • In addition, the N51 is equipped with Purge system pipes made from ‘optimized’ plastic, a feature that the N52 does not have.

These are some of the key differences between the N51 and N52 engines. Despite these design and mechanical distinctions, both engines yield the same power output.

So, what do “ULEV” and “SULEV” stand for? Let’s find out.

What Is ULEV and SULEV?

Credit: autowp.ru

The ULEV (Ultra Low Emission Vehicle) and SULEV (Super Ultra Low Emission Vehicle) are emission standards set for passenger vehicles in the U.S.

These classifications require vehicles to adhere to specific emissions standards compared to average gasoline vehicle models.


The ULEV or Ultra Low Emission Vehicle classification mandates that vehicles emit 50% fewer emissions than the average models available in a given year.

The ULEV standard surpasses the LEV (Low Emission Vehicle) standards but falls below the SULEV standard.


The SULEV or Super Ultra Low Emission Vehicle standard entails emissions that are 90% cleaner in terms of hydrocarbons, carbon monoxide, nitrous oxides, and other pollutants compared to average vehicle models.

SULEV goes beyond the LEV and ULEV standards but is not as stringent as the PZEV (partial zero-emissions vehicle) standard, which requires zero emissions from the vehicle.


Now that you have learned about the differences between N51 and N52, it’s important to note that both engines, despite their variations, offer the same power output of approximately 240 horsepower. Whether you prefer the N51 or N52 depends on your preference and budget, as both engines are excellent choices.

If you have experience owning either of these engines or both, feel free to share your personal insights in the comments section.


Is the N51 superior to the N52?

Both the N51 and N52 engines are designed to deliver the same output of 240 horsepower. However, the N51’s three-stage variable-length intake manifold (“DISA”) allows it to reach around 3,000 RPM. With all the information provided, the choice between the two ultimately depends on your specific needs and preferences.

Is the N51 engine dependable?

Yes, the N51 engine, like its counterpart the N52, is known for its reliability. However, similar to the N52, the N51 may also experience some common issues.

What type of engine is the N51?

The N51 is the SULEV version of the N52 engine, designed as a more environmentally friendly engine option. This engine was distributed in various parts of the U.S. to comply with SULEV regulations.

Does the N51 come with DISA valves?

Yes, the N51 is equipped with a DISA valve to enhance engine efficiency.

Does the N51 feature a three-stage manifold?

Yes, the N51 is outfitted with a three-stage intake manifold, contributing to its power output of approximately 240 horsepower.

What does SULEV BMW entail?

SULEV, or Super Ultra Low Emission Vehicle, is a U.S. classification for passenger vehicle emissions. SULEV vehicles emit emissions that are 90% cleaner than typical vehicle emissions.

Image Credit: Facebook

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