could someone tell me the exact weight of the MVVS 61-91 size tuned pipe, and what diameter the header pipe should be?

Also, what header lengths are required with this pipe for a "lowish" rpm setup on a 15cc engine? I'm looking at about 12.000 rpm max, probably less. I need a rather long header in my setup, and the MVVS pipe looks to have pretty short tuning length, so that's why I'm interested in it...less pipe = more header.

Thanks in advance.