2 Darts said

On the 64-66 273 Hi Po had a single exhaust because the TB X-member was notched only on the driver's side. The passenger side pipe would run under the X-member making it the lowest point of the underbody. Results are predictable.

If there is concern about maintaining good exhaust gas velocity and scavenging, going from a small to a larger pipe is bass akwards. IMO, better scavenging would result by starting with a 2¼" head pipe (like the super six) and muffler. Step the tail pipes down to 2 or 1 7/8 to the atmosphere.

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