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# Air flow of a rotary

### Tech Articles

Talk about engine building here. New products, tricky questions or showcase your work - If it's engine building related it's welcome here.

When calculating air flow of a rotary for a given rpm what number do you divide the rpm by to get air flow in cfm

I'm not sure what you're asking, air flow and how its measured doesn't change based on engine configurations. What does, is brake specific fuel consumption (efficiency).

If that's what you're asking about it's not a simply x on a piston equals y on a rotary, there are a few rules of thumb that I follow that have proven somewhat repeatable on my dyno if you're curious though I'm reluctant to just throw them out there without knowing exactly what you're asking for fear of someone taking it as gospel.

Cubic inches of engine ✖️Engine rpm➗2=

then take that result and divide by 1728 then the end result will be a number in cfm

i want to no what the equation is for a rotary do I just divide the engine rpm by 3 to get engine cycles?

No, it's still just an air pump, just double the displacement since that formula is for a 4 stroke. For a 13b 160(rpm) / 3456 = cfm.