I spoke with Two Brothers and they told me that their 4-2-1 system can be installed without removing the PAIR valve, however they did recomended removing it. They stated that the pipe would work better with the PAIR removed. My question is: Other than weight savings is there any reason to remove the PAIR valve if the after market exhaust will fit without its removal? An earlier thread stated that there was no HP gain by removing the PAIR only weight savings. Why would the pipe "work better" with the PAIR removed?