Horse power drop using early A 273 manifolds

toolmanmike said
Ya, look it up. From what I have read, no muffler on the early cars. Way too loud so Ma Mopar added a muffler. May be @65dartcharger can clarify.

Muffler in the 65 catalog. I think the resonator made all the racket. Also note the design of the Y, not what's available today. There are repops that are more of the merge collectors like the ones Cosgig had pics of. I think I'd take this over the merged style, no D shape pinch point per bank. Muff had unique part number in catalog, not shared with any other engine. Aluminized 2660-541 or zinc coated 2660-548. 2660-545 was part number for resonator.