I asked Nightrider the maker of the VIED & XIED why you need Xied FL-XIED-10 with the cat or FL-XIED-10TFF without the cat or why they recommend a 50% setting with the cat and 25% setting without the cat on the VIED. This was the reply I got: "Generally the VIED's want settings around the 25% rich area once the converter is removed. This is actually to compensate for reversion bringing fresh air to the sensors (which is seen as a lean mixture and actually adds some fuel), so the VIED needs to be 'turned down' some to compensate. The net effect is you are still running (and adjusting) to get the ECM to run in closed loop at 14.0:1, but you have to back off on the VIED settings to stabilize the voltage readings with the lower settings because of the fresh air that can get to the O2 sensors with the converter removed" So apparently removing the cat actually makes the bike run richer not leaner as most people believe. They also recommend the same changes as decatting the head pipe if you keep the cat in but change to slip-ons with larger then a 1.75" baffle.

 

I decided to go with V&H slipon twin slash they told me their wasn't a reason to buy the FP-3 until i make more changes .Im going to see how they sound and see if they cause any side effects at the point i might go with the FP-3