Jasma is a Blitz sub-ordinate company, kind of like Lightning Audio is a Rockford Fosgate product simply marketed as a different company, so your hard-earned dollars end up in the same hands.
My R33 GTS-t came to Australia with this exhaust already fitted (like most), and it is 3" in diameter turbo back, however it is very quiet, so I am of the assumption it is restrictive.
If your's is the same, and you're serious about kw, do what I'm doing - UPGRADE!
Lambros Hi-Tech Mufflers in Sydney claim 25rwkw from their 3" stainless turbo back system - that's impressive in anyone's language. They claim that it's not too bad on the ears, either.
Cost is around $2100 fitted in 2 1/2 hours.
Worth a thought...