Originally Posted by Quicksilvers

Good info here Nissan actually did a excellent job with their H pipe design and exhaust/muffler as far as design and being a “true” dual exhaust that flows well. The Nismo H pipe is manufactured by HKS and I would consider keeping it. The exhaust/muffler is more for sound really there is not a lot to gain there. The biggest restriction is the stock Nissan OEM catalytic converters and there is something to gain by switching in terms of power. The Nissan OEM headers are not a huge restriction in the exhaust system but, quite a bit can be gained by installing longtube headers if you have no emissions testing and have the extra coin to install them. Also a great way to remove restriction and be cost effective would be to install high flow catalytic converters or test pipes. Before purchasing exhaust you should listen to other people’s exhaust set ups in person on their Z or listen to exhaust clips on places like YouTube etc. I have had the AAM Competition HFC’s and test pipes installed they were a great bang for the buck.