I have a 70 240. Stock SU carbs, Hot Cam, headers with duel 2" pipes, two glass packs on each pipe, one pair under the floor pan, one pair at the rear, four total. The quad glass packs make up the back pressure at low end RPM but do not strangle it at top end. Sounds great at in low speed and really roars when you get on the gas. It dose not sound like any other car in town thats for sure! I have gained lots of power over the single big 3" pipe on it when I got it.