I am wondering what type of oil to use in my 72 454 . The car is never driven in the cold weather . I like the synthetic oil's but they are expensive . I used to run Castrol Syntec 10w-40 in my jet boat . Is synthetic oil suggested for older engines the motor put's out around 450 H.P. what is best 5w-30, 10w30, 10w40 or 20w50 , it rarely see's really hot weather either.I live in the Northeast.