'72 to '74 Type 4 Dual Quiet Pack Exhaust System, Rect. FlangeThis exhaust system is reasonably quiet, yet provides a good bump in power. It bolts right on to the early trapezoid style large 3 bolt flange that came on the '72 to '74 1700cc and 1800cc engines. 1 3 8" tubing diameter provides good low end torque. Split header design ("dual duals": one header per muffler on each side) can create a bit of a "flat spot" on some engines with dual carbs that can be difficult to tune out.