Summit Racing have a perforated cone - see their exhaust section.
www.summitracing.com
This I am told breaks the exhaust up. The total area of the holes equals the internal diameter of the pipes which does not restrict flow.
It may be worth dropping Aussie Mike on the forum a PM, as he has experimented with exhausts - building a high quality side pipe system for my Cobra. You will find him on the Dark Side forum on the right of the main clubcobra page also..
