at first you ll do just fine with 2.5" piping, but later down the road as you start to build the motor and upgrade the turbo and its related parts. you will want to go with a 3" system. We have customers who order 2.5" custom mandrel systems and love them and then later when they have made several upgrades they come back for 3" and love the gains.. they report and say how they get better spool and better throttle response.. pretty cheap to compared to the 500+ systems of Thermal and others.