SQL & PL/SQL

hi

I have a 83 character string, i am using this query to split it in two strings

select substr(s_string, 1, trunc(length(s_string) / 2)) || ' ' ||
substr(s_string, trunc((length(s_string / 2))) + 1) from dual;

it will split in two strings of one with 41 characters,space and the remaining characters.

suppose if i am having 183 characters this query will split in two strings one with 91 characters,space and remaining characters.

but i want the length of the two strings should be less than 80 whatever be the I/p string length.i/p string length can be greater than 200 also but it should split in such a manner that o/p strings must have length less than 80.

kindly helme with this issue