when i had my 2.5 i never ussed a timing light, just kept advancing it little by little till it pinged then knocked it back a little bit. be careful though, pinging = bad. The more advanced your timing is the more power ur car will make, just how advanced u can run it will depend on fuel, and ambient temp and stuff, best do it at the hottest time of the year, then u know it will always be right.