I was wondering has anyone here installed Twice Pipes with stock header?

How does it sound? Still loud? I really don't want to pay 300+ for aftermarket header if it doesn't improve performance much. But I do want some nice sound

I installed the twice pipes with my stock header on my 78 280z.

It sounds awesome. Not obnoxious Honda loud, but definitely attention grabbing, and a great bubbling when coasting or idling.

I heard they don't do anymore for performance then a larger exhaust.

I can't comment on improved performance, the twice pipes went on during my engine rebuild, and while my car is definitely stronger, I don't know how much is due to the exhaust. I'v seen lots of info on exhaust options here and over at HybridZ, when I was over there, if you need comparisons...