Why is the piping from the cat side to the resonator is ID 2", OD ~2.25" whereas it get larger as it goes to the canister after the resonator? I thought the Mugen exhaust is 2.5" throughout. Also, is the whole system stainless steel?

 

The full system is stainless steel. The "loop" is a little smaller than 2.5" as well.

 

Was told before that the the reason for the smaller piping in the front was to create torque for lightly moded cars... but for me I had moded the pipe to a 2.5" ID and the mids to high feels a lot better. Future plans, I am thinking of doing a 2.5" mandrel bent pipe all the way through to muffler to see if I can squeeze a lil more out of her. I am running on JUN3 cams with stock bottom for now