I have 1965 Belvedere with 440 dual exhaust 2.5 inch. I can't decide which will sound the best. I love the deep rumble outside the car. Don't want it to be to loud inside the car. Yet I do want people to know I'm a coming. Can get a good deal on the super40 not so good on the 50 series. Advasnced suto is offering 20% off if you buy them online before 5/28/2011