Cubic Inches

does anyone know how to figure out cubic inches i would like to know how many inches i can put extra on my soon to be car Mazda Rx-7 used with 50000 miles on it

http://www.fordfans1.homestead.com/FORDFAN1.html

Enlarging a rotary engine isn't as easy as it is in a piston engine. There's a formula for displacement in a rotary, but htat too is more complicated than the simple formula for a piston engine.

It's better to turbocharge it.