i called kawell earlier to talk to him about that. give him a call and talk to him, you cant go wrong!
i am using 2.25 right now. dont knowif it is to big but its what i have. if i had to buy another one i would make it 2" out as my turbo is 2" out and prob do the same into the end castings. smaller tubing = more velocity, less time to fill. (prob talking nano seconds)