NA is louder than turbo, much louder.
Mine is NA, zx4 2006 2.0 with cams, cosworth IM, CAI, OBX header, full 2.5" exhaust with three magnaflows and it's still loud. It would be a sleeper if wasn't loud. It's tuned by Tom with SCT, rev up to 7800rpm.
2 years with this setup. Now I'm going for turbo.