Why is the formula for finding cubic inches of an engine .7854 x bore x bore x stroke x # of cylinders?

Answer 1

http://en.wikipedia.org/wiki/Engine_displacement

Formula for area of a circle is typically A = (pi * r^2)
However the bore is the diameter (D)

And the diameter D = 2 * radius OR radius = D/2

Placing this into the area formula above gives A = (pi * (D/2)^2).
Some mathematical simplification:
A = (pi * (D^2)/(2^2)) = (pi * (D^2)/4)
So A = pi/4 * D^2

But D is just the bore so
A = pi/4 * (Bore)^2

pi/4 is approx .7854

So the displacement of one cylinder is the area of the piston * the stroke = .7854 * Bore * Bore * Stroke

Total displacement is then the above multiplied by the number of cylinders or your given formula.

Answer 2

Cubic Inch Displacement Formula

Answer 3

Look on the block- it's already been formulated for you!