wrote

The Aeronca muff often involved a deflector plate, attached to a small
strut across the pipe vee, that prevented the air from travelling
straight across the chamber from the inlet to the outlet. The
deflector made the air flow around the pipes to get from one side to
the other. Lots more heat. Does your have that?

How about a diverter shaped to make the air corkscrew around the pipe?
--
Jim in NC