RE: O.S. 46 FX on a pipe
I wouldn't move the pressure tap , you can count on rossi and novarossi etc and nelson engines to know where to place a tap for pressure and they often place the tap on the header much like yours is, if you own a nelson ultrathrust muffler take a look at their placement of their pressure tap..... you will find that you will have to take at least two or more inches off the header length to be in the right resonance.