calculating throttle body size.

Hi All,
 
I am fabricating an inlet manifold for a turbocharged 2 litre Escort.
Plan is for 1 to 1.5 bar boost.
The car will NOT have an intercooler.
If the turbo outlet is 41mm inside diameter how do you calculate the inside diameter of the throttle body?
That is, what should be the inside diameter of the throttle body?
My thinking is I should be using a throttle body from a 4 litre car.
 
Thanks!