I have a 2014 FLHX and removed the cat from the header pipe and a set of Screaming Eagles. Now I am thinking of putting on a S&S or Vance & Hines header pipe. Will it make any difference being that the pipe I have on there is a stock header pipe?

 

The difference would be the location of the O2 sensors. The aftermarket pipes are designed to run without the CAT unlike the stock head pipe.

 

As the previous poster said, the stock pipes have the O2 sensors located to run WITH the cat. What frequently happens is if you remove the cat, the O2 sensors often have trouble properly adjusting as they "crosstalk" as it's called. They are located too close to one another to run that way. My V&H Power Duals are a 2-1-2 like the OEM exhaust but the rear O2 is much higher in the pipe to prevent that.

 

Curious how the removal of the cat could cause crosstalk. The subject has come up in the past but it doesn't make sense to me. The 02 sensors are still the same distance from the exhaust port and read what is exiting the ports.
Plenty have removed the cat and don't seem to have issues. I suppose if they added a tuner it would answer that question.
Not denying there may be an issue, just trying to understand.