OEM Air Filter Air Flow: 42.40 CFM. DNA Air Filter Air Flow: 60.40 CFM. DNA Increased Air Flow: +42.46%. DNA Filtering Efficiency: 98-99%. This filter features DNA’s Round Design. Installation of the filter is very easy, simply follow the information that can be found in the Royal Enfield workshop manual. The filtering efficiency is extremely high at 98-99% filtering efficiency, with 4 layers of DNA Cotton. The flow of this DNA filter set is 42.46% more than the Royal Enfield stock paper filter. This DNA filter is designed as a High flow Air filter for:’Road & Race use’. OEM Air Filter Air Flow: 30.90 CFM. DNA Increased Air Flow: +95.47%. This filter features DNA®’s Stage 2 kit eliminates the OEM intake snorkel of the Royal Enfield 650 and offers higher performance and better intake sound. This Stage 2 kit is designed to work exclusively with the DNA R-RE65N18-01 air filter. Performance wise, up to + 6 whp can be offered from our Stage 2 kit for the Royal Enfield with the proper ECU tune. The flow of this DNA filter set is 95.47% more than the Royal Enfield stock paper filter. This DNA filter is designed as a High flow Air filter for:’Race use’. Fuel recalibration is suggested.