Exhaust pipe size

I have dynomax headers an my 318 an i love them http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=1283&prmenbr=361 i think its a good price too,only draw back is the car needs manual streering,an i hate changing the damn plugs on the dside,the ground clea.isnt the best but all other brands for small blocks are the same on the d side other then tti's
MIKE