What does a 90 cubic inch harley motorconvert to in cc's?

A few tricks, first and foremost to get the specific answer with the specific given information of 90 Cubic Inches

-A cubic inch is 16.387064 cubic centimeters, (CC)-

you multiply 16.387064 x 90(your Cubic Inches of motor) = 1474.83576 (CCs)

Or if you know that you have a 1.5 Liter Motor, as according to your factory build OEM Manual, you can take the decimal point to the right three times to equal 1400 (CCs) .... so 1.5(L)=1500(CC)s -This is of course not the engineering spec but rather A close estimate usually given to the consumer.