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# Air density equation

### EFI Tuning Fundamentals

Discussion and questions related to the course EFI Tuning Fundamentals

Page 1

air density can be calculated by the equation D=(2.7xP)/T. The equation is very simple but what is bugging me a little is that i dont understand the constant, the 2.7. why is it 2.7, where did it come from?

It's a fair question. I've gone into this in a little more detail in the about to be released reshoot of this course but here's the reason:

The equation for air density is: Density = Pressure / R x T

R is the specific gas constant which equals 53.35 so this ends up on the bottom of the equation. P for this example is measured in pounds per square inch, but we need to change this to units of square feet since we're calculating air density in pounds per square foot. To convert from square inches to square feet, we need to multiply by 144 since there are 144 square inches in a square foot.

So forgetting about temp and pressure for a moment we end up with 144 / 53.25 which is equal to 2.7. This gives us the constant of 2.7 in the equation :)

ahhh thank you very much. I was looking into gas constants and i tried plugging in all sorts of numbers.. for instance i found a gas constant for .83 but that was g/L and converted to lb/ft3 it didnt make any sense. and a few others, i was very confused so Thanks

ahhh thank you very much. I was looking into gas constants and i tried plugging in all sorts of numbers.. for instance i found a gas constant for .83 but that was g/L and converted to lb/ft3 it didnt make any sense. and a few others, i was very confused so Thanks