MicroSquirt.com read only forum (Jan.15,2018)

If you're running four throttles and need 3.25 sq. in. then each one
needs to be 3.25/4 or ~0.81 sq. in.

area is pi times the radius squared, so 0.81 = 3.14 * r^2.

Then r^2 = 0.81/3.14, which is about 0.26 (rounding up), and r = sq
root of 0.26 which is just over 0.5". So the radius is 0.5" and ...