Also found this when reading up on the supersprint system,they also mention about having one of the systems at 54mm bore to stop inside drone noise,and there group N at 63.5mm.
Front section with HJS 100 CPSI sports cat or with resonator (to avoid the typical metallic buzz of decat pipes). Ø60mm for optimal flow, compatible with OEM headers and centre pipe.
-Resonated centre section Ø54mm, to avoid drone inside the cabine
-Rear muffler Ø54mm, homologated, available in "stealth" version, hidden behind the bumper like the stock system, or with a 120x80mm oval tip under the bumper (no need to cut)
This exhaust has been developed to give optimal performance gains without being too loud and drony for daily commute and highway driving. The HJS metallic cat reduce the pollutant gas perfectly.
A version for the 182 '04-'05 version bumper, with twin central outlets, is available
The racing "Group N" exhaust, Ø 63.5mm / 2"5, is designed for race cars and trackdays, so both the front and centre sections are available in unresonated straight pipe version. The rear silencer is available with a simple Ø70mm outlet under the bumper or as a "stealth" version.