? on headers
 

what is the diff between 4-1 one piece and 421 one piece these are dc headers whichhttp://www.wholesalehyperformance.com/heads.html one do i get for my car

4-1 is more for top end power.
4-2-1 is more balanced throughout the rpm range.
you can get either one - depends what you want.

well which one is better which gives more HP and better for your car

Go for the 4-2-1 they're best for the street. Don't expect a big gain from either though, its just a link in the intake/header/exhaust chain which together will give you about 20HP plus or minus a few.