I had these, couldnt fault them.
http://www.ebay.co.uk/itm/NISSAN-350Z-Z33-3-5L-EXHAUST-DE-CAT-PIPE-DECAT-PIPES-SILENCED-/320816230213?hash=item4ab2232f45
both claim 99, in a lab test, shell (before nitro+) showed to be a 98 where as tesco showed a true 99. also i mapped my honda twice, once on each fuel, the mapper said the curve was much smoother using momentum!? i always use momentum