BS4 vs BS6: Key Differences, Benefits and Impact on Bikes

What Are BS4 and BS6 Emission Norms?

Bharat Stage (BS) emission norms are standards prescribed to control pollutants emitted by motor vehicles in India. They specify permissible emission limits for pollutants such as carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx) and particulate matter (PM).

BS4 was an earlier emission standard. BS6 introduced substantially stricter emission requirements and required vehicle manufacturers to use improved technologies to control emissions. BS6 emission norms are stricter than the BS4 criteria and help to reduce NOx emissions by 70% in diesel two-wheelers and by 25% for petrol engines. Thus, a BS6 engine emits five times lower sulphur traces than a BS4 engine.

The transition from BS4 to BS6 was significant for the two-wheeler industry because manufacturers had to redesign or recalibrate engines and adopt technologies such as electronic fuel injection and onboard diagnostics.

BS4 vs BS6: Key Differences

The main difference between BS4 and BS6 is that BS6 sets stricter emission requirements and requires more advanced emission-control technology.

1. Emission Limits

   BS6 has stricter limits for pollutants than BS4. The objective is to reduce emissions of NOx, hydrocarbons, carbon monoxide and particulate matter from vehicles. For two-wheelers, this meant manufacturers had to improve combustion and exhaust-treatment systems to meet the newer limits.

2. Fuel Quality

   BS6 was introduced alongside BS6-grade fuel, which has a significantly lower sulphur content than BS4 fuel. Lower sulphur fuel supports modern emission-control systems and cleaner combustion.

3. Fuel Injection

   Many BS4 two-wheelers, particularly older and smaller models, used carburettors. BS6-compliant models generally adopted electronic fuel injection to achieve more precise control over the air-fuel mixture. Fuel injection can improve combustion control, throttle response and fuel efficiency, although actual mileage depends on the specific bike and riding conditions.

4. On-Board Diagnostics (OBD)

   BS6 introduced stricter onboard diagnostic requirements. OBD systems monitor various vehicle parameters and can help identify faults affecting emissions and engine operation. Later regulatory updates further strengthened onboard monitoring requirements for vehicles.

5. Emission-Control Technology

   BS6-compliant two-wheelers use improved emission-control components and engine calibration to meet stricter limits. Depending on the vehicle, this can include improved catalytic converters, fuel-injection systems and other emission-control technologies.

BS4 vs BS6: Engine Pollution Emission Level Comparison

The B6 engine emits fewer pollutants than the BS4 engine. The table below depicts the emission levels of both BS6 and BS4 engines.

BS6 allows lower emissions than BS4 and requires manufacturers to use technology capable of meeting those tighter limits.

How Does a BS6 Engine Work?

Given the high pollution levels in India, the BS4 norms, despite being stringent, were insufficient. The BS6 norms introduced by MoRTH are expected to reduce NOx and PM levels, as well as sulphur traces.

The BS6 norms also claim to reduce NOx levels by 25% in petrol engines and by 68% in diesel engines. It is also anticipated that PM emissions from diesel vehicles will fall by 80%.

In the BS6 engine, the converter assists the Selective Catalytic Reduction (SCR) mechanism in reducing nitrogen oxides to Diatomic Nitrogen or H2O. In this, the SCR system uses a fuel-fume fluid to minimise NOx levels.

If exhaust fumes come into contact with AdBlue, the urea is converted into CO2 or ammonia. NOx is also converted to nitrogen and water vapour, which helps minimise emissions.

Why Do We Need a BS6 Bike Engine?

With advancements in engine technology, BS6 has made significant improvements across every aspect. Under this norm, two-wheeler manufacturers must install gasoline injection systems to reduce toxic exhaust emissions.

As BS6 bike engines are more powerful and more fuel-efficient, they have reduced carbon emissions. Ultimately, this emission norm has improved the overall performance of a two-wheeler.

How Did BS6 Change Two-Wheeler Engines?

The transition to BS6 required manufacturers to make several changes to petrol two-wheelers.

1. Electronic Fuel Injection

   Fuel injection replaced carburettors in many models because it can deliver a more precisely controlled air-fuel mixture. This helps the engine achieve cleaner and more consistent combustion.

2. Improved Catalytic Conversion

   Catalytic converters help reduce harmful pollutants in exhaust gases before they leave the vehicle. BS6-compliant vehicles use improved emission-control systems to meet the tighter standards.

3. Engine Calibration

   Manufacturers had to recalibrate engines and optimise combustion parameters to meet BS6 emission requirements. This could affect throttle response, power delivery and fuel efficiency depending on the model.

4. Onboard Diagnostics

   BS6-compliant vehicles use onboard diagnostic systems to monitor relevant vehicle systems and identify certain faults.

Impact of BS6 on Two-Wheelers

The transition to BS6 affected both manufacturers and consumers.

1. Higher Manufacturing Costs

   Manufacturers had to invest in new technologies, testing, calibration and emission-control equipment. This increased the cost of producing many BS6-compliant two-wheelers.

   As a result, several models became more expensive compared with their BS4 predecessors.

2. Changes in Bike Prices

   The addition of fuel-injection systems, improved catalytic converters, diagnostic systems and other components contributed to higher vehicle prices.

   However, the exact price difference varies by manufacturer, model and engine capacity. Therefore, a fixed percentage increase should not be applied to every BS6 bike.

3. Changes in Mileage

   BS6 technology does not automatically mean that every bike will deliver higher mileage. However, electronic fuel injection can provide more precise fuel delivery and may contribute to efficient combustion.

   Actual mileage depends on factors such as engine capacity, riding style, traffic, maintenance, tyre pressure and road conditions.

4. Changes in Performance

   Some early BS6 models were perceived as having slightly different throttle response or power delivery compared with their BS4 versions because manufacturers had to balance performance with stricter emission requirements.

   Modern BS6-compliant motorcycles are designed to provide a balance between performance, drivability and emission control.

5. More Advanced Maintenance

   BS6 motorcycles contain more electronic and emission-control components than many older BS4 models. This can make diagnosis and repair more technology-dependent.

   Regular servicing, using the recommended engine oil and maintaining the fuel and emission-control systems are important for keeping a BS6 bike running properly.

What is BS6 Phase 2?

BS6 Phase 2 introduced additional emission and monitoring requirements for vehicles in India as of April 2023.

For applicable vehicles, the updated requirements strengthened onboard diagnostics and emission monitoring. The transition is part of India's continuing effort to make vehicle emission standards more stringent.

For consumers, this means newer two-wheelers may have more sophisticated electronic monitoring and emission-control systems than the first generation of BS6 vehicles.

Can You Still Ride a BS4 Bike?

Yes. The introduction of BS6 did not make existing, legally registered BS4 bikes automatically illegal. The BS6 transition primarily affected the manufacture, sale and registration of new vehicles after the applicable deadline. An existing BS4 bike can generally continue to be used as long as it is legally registered and complies with applicable vehicle, insurance and pollution-control requirements.

Local restrictions can apply in specific areas or under particular pollution-control measures, so owners should follow the rules applicable to their location.

How to Check Whether Your Bike Is BS4 or BS6?

You can check your bike's emission standard in the vehicle documents and records. Some ways to identify it include:

• Check the vehicle's Registration Certificate (RC).
• Check the manufacturer's documentation or specifications.
• Look for the emission-standard information provided with the vehicle.
• Check the vehicle details through official transport records where applicable.
• Contact the authorised manufacturer/dealer if the information is unclear.

The manufacturing year alone should not be used to identify the emission standard, as the transition period and individual vehicle records can vary.

Does BS6 Affect Bike Insurance?

BS4 or BS6 compliance does not requires a separate type of bike insurance policy. However, the vehicle's make, model, age, engine capacity, IDV, location and other factors can influence the two-wheeler insurance premium. A newer BS6 bike may have a higher purchase price and IDV than an older BS4 bike, which can affect the cost of own-damage bike insurance.

Regardless of whether the bike is BS4 or BS6, a valid third-party bike insurance policy is mandatory for riding on Indian public roads.

FAQs - BS4 vs BS6 Bikes