Beet Exhaust ( not complete ...)

[zxr400l3]

Hi there, i have only the headers of the beed exhaust, its too hard to find only the downpipe, so i decided to make it ... if someone have it pictured from close distance will be great, also i want to ask, what size pipe to use, how long also ... if i shorten it too much, what i loose? i am thinking to make it short with stubby end can ... but i am afraid i will lose power ... if someone can explain what are the benefits of the long downpipe ... will be great, i am sure its better with long, because on all race bikes i see its long ... but i want to look like the ducati ... only small piece of tube shows from the fairing down ...