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# Volumetric efficiency calculation

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 gpara (Automotive) 11 May 09 20:03
 Can someone give me a volumetric efficiency formula to calculate the cubic feet per minute volume of and engine at a given RPM???
 patprimmer (Publican) 11 May 09 20:27
 UmmmmThe actual volume of air at ambient temperature amd pressure vs the theoretical displacement.Like 400 CI 4 stroke displaces 200 CI per turn of the engine in theory, but actually draws in 180 CI per turn is 90% VE RegardsPatSee FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &http://eng-tips.com/market.cfmfor site rules
 BrianPetersen (Mechanical) 11 May 09 21:34
 The original poster needs to clarify the question."Nominal displacement" (converted to the units of your choice) x half (because of 4 stroke engine) x revolutions per minute x volumetric efficiency under the specific conditions involved = volume rate of flow.The trouble is that the volumetric efficiency depends on a TON of variables and can often only be estimated. How accurate the estimate needs to be, and how much effort and calculation and simulation needs to be put into producing that estimate, depends on what you are doing with the outcome, and THAT is something you haven't told us.
 IceStationZebra (Mechanical) 11 May 09 21:37
 for a 4 stroke engine:displacement (cubic inches) x  RPM x vol eff%---------------------------------------------   =  CFM                3456displacement (liters) x  RPM x vol eff%---------------------------------------   =  CFM                56.633692 stroke:displacement (liters) x  RPM x vol eff%---------------------------------------  =  CFM                28.31685ISZ
 gpara (Automotive) 12 May 09 8:34
 Thanks Guys

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