im running a y8 in my rex, mild head work dc 4 - 1 headers, full 2 1/2 cat back. injen 3" intake with k & n filter, and im running a stock p28. is there any suggestion to what spark plug i should use.. hotter or colder than stock?

 

Stock.
Your mods don't require a colder plug.
Add nitrous, a turbo, or some high compression pistions and then you need to go for a colder plug.