Difference Between BS4 and BS6 Engines

Bharat Stage Emission Standards (BSES) were implemented to control the harmful gases emitted from the exhaust of the vehicle. 

BS4 norms came into effect in 2017 with stricter emission standards than BS2 and BS3. The most visible change was the Automatic Headlamp On (AHO). The norm catered to the safety aspects. Other norms included tailpipe emissions, the Electronic Control Unit (ECU), ignition control, etc.

The government decided to skip BS5 and straight away brought in BS6 norms. These new norms set a stricter limit for the pollutants coming out of the vehicle’s exhaust. BS6 norms mainly focus on reducing emissions of NOx gas and particulate matter which cause air pollution. 

Main Differences between BS4 and BS6 Engines

  • A vital difference between BS6 and BS4 is that BS6 fuel contains 5 times fewer (10 ppm) Sulphur traces. 
  • NOx level will be brought down by a staggering 70% in Diesel engines and 25% in Petrol engines. 
  • Real Driving Emissions (RDE) will be introduced in India for the first time with the implementation of BS6 norms. It will measure the vehicle’s emission in real-world against the stimulated conditions. 
  • Diesel Particulate Filters (DPF) are being introduced for particular matter reduction in diesel engines. It functions to remove soot from the gas of the exhaust of the diesel engine.
  • The automakers will also have to put catalytic converters for Selective Catalytic Reduction (SCR). Catalytic converters reduce toxic gases and pollutants from an internal combustion engine by catalyzing a redox reaction.
  • The new vehicles according to the BS6 norms should have an onboard diagnostic system to monitor that the prescribed equipment is working properly. This feature is essential, considering the car manufacturers in the past tried to alter the results of pollution generated from their products.

All these systems have to be put into cars from the year 2020. As soon as the lockdown ends and the industry begins to manufacture new products, we will get to see the high-tech BS6 engines and cars.


  • There is also a major difference in the prices. The prices of BS6 models have been increased
  • The New Honda Shine BS6 is priced at ₹67,857 whereas the price of BS4 was ₹59,990. 
  • The New Honda Amaze BS6 is priced at ₹6.10 lakhs whereas the price of BS4 model was 5.93 lakhs.
  • The price of BS6 Hero Splendor starts from ₹59,600 whereas the earlier price of BS4 model was ₹53,000

Advantages of BS6 over BS4

  • Bharat Stage 6 (BS6) is the most advanced emission standard for automobiles around the world. 
  • It is equivalent to Euro-6 norms, thus setting high competitive standards for the Indian automotive industry.
  • BS6 norms are capable of bringing down emission levels by 51%.
  • The BS6 engines minimize the fuel consumption as the cars are tuned to run on the current stoichiometric air-fuel mixture.

Reduction of pollutants in the air will build a better atmosphere for humans. It will be beneficial for our health. The journey from BS4 to BS6 was very time consuming, but the standards were worth the wait.

Avatar photo
Mechanical Engineer and a Passionate Writer