it will not hurt power negatively peak # wise. if anything youll definately gain there. but it may take the motor a while to catch up to a huge throttle body, and therefor youll more than likely lose some power under the curve. i have a 65mm tb on my setup and i love the way it runs. i would agree with the rest. 65mm on the inside is the biggest id go. i think mine is 68-70mm at the intake, and 65mm at the manifold opening and matches my skunk2 manifold perfectly.