You did not say what mods you have only the you WANT downpipes. If you are not FBO you don't NEED them so its a waste of time & money. Any number of cars are in the low 12's high 11's without aftermarket downpipes.
Also you did not say what state you are in, DP's will not pass most emission tests.
2013 135is Cab JB4/ISO - 2011 335is JB4/ISO/BMS Flash - 2009 V-Star
2009 Ford Expedition EL 4X4 - 2003 Xterra 4X4 - 1998 Ranger 4X4 - FFR Cobra MK-IV work in progress