Had my bike dyno'd yesterday by Andy at Junction 33 Dyno Center and was given some usefull pointers towards big V twin exhaust design as he used to work for Quill Exhausts. The bit that interests us the most is re packing the silencers, especially to increase the life of carbon sleeves. The perforated tube inside should first be wrapped in stainless steel wool then overwrapped with the packing fiber. The wire wool protects the packing from destruction by the strong pulses in a V twins exhaust and it was evident in my end cans that this was missing. With less than a thousand miles under my belt with them the sleeves need replacing as they show distinct burn rings around the inlet. I havs just ordered two carbon sleeves and packing from PJ engineering in Lincolnshire and 4m of 4" wide wire wool off ebay, total cost £115 . Its a double heads up really, firstly make sure you buy pucka exhausts from a reputable source and secondly how to pack and where to get the bits from.
hope this helps, wish i had read it 9 months ago