Exhaust pipe size after headers

[super vw]

Hey guys, i need to start thinking about what size pipe i need to get in order to make my exhaust. I have a Kymco 1 5/8 header im using for my 1914cc N/A motor.

I will be useing two glass pack style mufflers (dynomax, flowmaster... not sure yet) in series (one after another, single outlet). Whats the best size to use keeping in mind im looking for the most torq.

Thanks!
Jonathan