You can do whatever you want I suppose but high-flow pipes without highflow aircleaner is like putting a fan next to a closed window (just made that one up myself by the way). It can't breath right unless you open bothe ends of the engine. You can however skip the ECM recalibration ....just be sure to use the PC map for the stock ECM. All the recal. gets you is a slightly higher RPM rev limit which is of little use on the street. PC doesn't care what ECM you have as long as you tell it which one.