Air Filter Flow Calculations Chuck Leeper with permission from K&N Introduction Below is a series of formulas to determine air filter size for a given air flow capacity. Chuck was trouble shooting a problem when he found that air flow he needed was more than his 9" filter could provide. K&N shared this information with him to help trouble shoot his problem. Formulas Square inches of filter required for a motor = CID x Maximum RPM / 20839 CFM required for a 4 stroke motor = CID x Maximum RPM / 3456 CFM required for a 2 stroke motor = CID x Maximum RPM / 1728 CFM required for a turbocharged or supercharged motor = Pounds of Boost / 14.7 Add 1.0 to this answer. This relates to #2 and #3 Example: (CID x maximum RPM x #4 ) / 3456 or 1728 To find circumference of a circle multiply diameter by 3.1416 To find diameter of a circle multiply circumference by .31831 CFM Formulas for Filters Round: Diameter x Height x 6 x 3.14 Flat Panel: Length x Width x 6 Universal Round Taper: (Base + Top) / 2 = A Take A x Length x 6 x 3.14 Universal Round Straight: Diameter x Length x 6 x 3.14

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