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What is the Difference Between BS4 and BS6 Engine?

Published on January 01, 2023 by BikeJunction

Since the age of industrialisation, massive carbon emission has raised pollution and global temperature. When we burn any fossil fuel, either solid or liquid, some gases are hazardous to our health and Environment. The purpose of writing the blog on BS4 vs BS6 Motorcycles is to clarify the pollutant which is being emitted from our Motorcycles. 

The Government has been concerned about these hazardous emissions from motorbikes and cars, which is why they set regulations on emission standards with the name Bharat Stage(BS) which was introduced in the year 2000. The Second Bharat stage (BS2) rules were introduced in the year 2005 which was inspired by Euro 2 regulation in Europe. The latest regulations were implied by the Government of India in 2020 April which is known as Bharat Stage VI(BS6). While going with the blog further, you will find details about the emission standards and the difference between BS6 and BS4 along with the difference between BS4 and BS6 mileage.

The Oil Industry Safety Directorate is a technical directorate under the Government of India and falls under the Ministry of Petroleum & Natural Gas.
To understand the difference between BS4 & BS6 models, we need to know about the agency which works in developing standards and implementing them, along with time-to-time audits. Oil and gas installations to check their compliance from time to time. The difference between BS4 and BS6 models in the bikes industry brings a lot of challenges for manufacturers. Comparing BS4 and BS6 models will certainly highlight the need for emission regulation norms in today's time.

Skipping of BS5 norms and its impact on the automobile industry

Reportedly, as per the previous fuel policy of the Government, the BS2 and BS3 regulations had to be replaced with BS4 norms with effect to the latest by 1st April 2017. The committee suggested introducing the BS5 norms latest by 1st April 2020 and the BS6 norms followed by it in the year 2024. However, the rising pollution in the country forced the Government to leapfrog BS5 norms, and they introduced BS6 norms, directly skipping a level. This way, BS6 norms were introduced on 1st April 2020.

When the news came out that the Government of India was rolling out BS6 norms on 1st April 2020, skipping BS5 regulations, there was chaos in the industry. It had been witnessed that it created a huge price drop, and discount offers were given on BS4-compatible engines. Many were not knowing the scenario, shall they wait or avail of the offers. It was a difficult time for everyone, from manufacturers to customers. Some big brands offered a good amount of discount, and few of them showed a slight move. 

BS6 compatible engines and their performance

As discussed above, the provision of introducing BS4 in place of BS6 was to curb the rapidly rising pollution. If it has to be explained in layman's terms, the BS4 engines will require fuel containing a lesser amount of Sulphur than 10 ppm, so it will be more Environmentally friendly with the least hazardous emission. Now, the challenge customers have to face is this compatibility, and an environment-friendly model will impact the vehicle's performance. Furthermore, to maintain performance, manufacturers have to increase the engine's displacement, which will further increase the price range of the vehicle. Therefore, the BS6 models will be costlier than the BS4 model bikes/scooters. 

As yet, the Government is wondering how to take out the middle path to curb the pollution caused by the automobile sector without any effect on the performance of bikes/scooters. This is the main reason why the Government of India is more focused towards Electric vehicles.

The Indian Government developed Bharat Stage Emission Standards to restrict the increased pollution around us, especially in metropolitan cities emitted by internal combustion.

There are several such norms around the world. For example, let's talk about Europe. The European standard focuses on reducing not only Sulphur but Nitrogen oxides, carbon oxides, and sulphur oxides from diesel and petrol variants. 

Parallel, the BS6 standard will help to reduce sulphur levels. Also, it includes the provisions to reduce Nitric oxide and particulate matter levels (PM Level). In addition, these standards will restrict the emission of Carbon Oxides to 1.0g/km.

BS4 and BS6 difference that reduced the pollutants


Difference BS6 vs BS4 engine


The BS4-compatible engines of bikes and cars were a little cheap in the market and were prone to cause more pollution. As BS6 restricts the manufacturer in many ways, it has caused a challenge to the manufacturer to upgrade their product following the set norms. Until now, there is no information about BS7, but the rising pollution is another signal towards the same. Further talking about the mileage difference between BS4 and BS6. There is no such difference in the mileage but slight variations can be felt which will not impact your pocket much. In some cases BS4 may produce little more mileage than BS6 and vice versa. 

BS4 restrictions are as follows

It cannot discharge more than 80mg/km of Nitrogen oxide in the case of a Motorbike and 250mg/km for a diesel vehicle. 
Sulphur content could be 50 ppm in BS6.

SCR(Selective Catalytic Reduction) and DPF(Diesel particulate Filter) were not mentioned to be measured in BS4; however, they are considered in BS6
Onboard Diagnostic(OD) was not required in BS4 but is necessary in BS6.

Detailed History of emission norms in India

Standard Reference Year Region
Petrol Norms N/A 1991 Nationwide
Diesel Norms N/A 1992 Nationwide
India 2000 (BS1) Euro 1 2000 Nationwide
Bharat Stage II (BS2) Euro 2


April 2003

April 2005

NCR, Mumbai, Kolkata, Chennai

NCR with 13 Cities


 Bharat Stage III (BS3) Euro 3

April 2005

April 2010

NCR with 13 cities


Bharat Stage IV (BS4) Euro 4

April 2010

April 2017

NCR with 13 cities


Bharat Stage V (BS5) Euro 5 Skipped  
Bharat Stage VI (BS6) Euro 6 April 2020 Nationwide


Current Scenario of emission standard in the country

Recently, the Government of India constituted an expert committee under the supervision of NITI aayog to develop auto fuel vision and policy 2025. The basic idea behind the formation of this committee is to prepare a road map for fuel consumption and maintain its non-hazardous emission.

Suppose existing policies of emission norms(Bharat stage) could be discussed briefly. In that case, the analysis will show how Government policies are continuously trying to make the fuel more pollution-free by decreasing the ppm(parts per million of permissible Sulphur).

The Fuel quality has been significantly improved from BS4 to BS6 regularisation by reducing the permissible Sulphur content to a maximum of 10 ppm(parts per million) in BS6-compliant fuel, which was 50 ppm(parts per million) in BS4. In addition, with the introduction of BS4, many advanced emission control technologies were introduced, including Diesel particulate filters and Selective catalyst reduction systems to reduce particulate matter and emission of Nitrogen oxide.

Several operational and functional procedures have been established under the Health safety and environment Management System. However, most of the time, HSSE projects and works are scrutinised by the top authority, which is particularly oriented towards the project needs, related guidelines and job competency requirements.

What we can learn from BS6 vs BS4 Norms

Based on the above data, we have keenly observed and evaluated that technology at the cost of the Environment will never be sustainable. The next norm may bring more environment-friendly regulations, and the bs4 vs bs6 bike price difference will increase in the same ratio. If we talk about the country's capital city, Delhi Government had to implement an odd-even formula for vehicles to control and reduce pollution. These days many governments are setting up air filtration towers at the centre of the cities so that citizens can breathe healthily, as the data above shows how dangerous sulphur oxide is. Differences between BS4 and BS6 bikes are mostly the bike's cost, the motorcycle's performance and the sulphur factor.

Further, the difference between BS4 and BS6 vehicles is not limited to bikes, but they are similarly applicable to cars. Different people have different opinions about which is better, BS4 or BS6 vehicles. As aware citizens of the country, we must be informed that there is a limit to fuels and petroleum in the world. We must create a manageable future for our future generation. We should obey the norms and minimise the age of pollution from our end. The Earth was clean and green when human life started, and now, especially after industrialisation, we humans have become the major cause of global warming and rising pollution.

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