Exhaust Pipe

The exhaust pipe is an area where signifcant weight can be saved.  I know that Dax makes a beautiful stainless steel unit, but this for my purposes is just too heavy.  I want to make mine according to the same design, but out of thinner walled stainless steel ( the pipe) and the silencer out of Aluminium or even carbon fibre.  In additoin to this, I want my pipe to have 2 set-ups, namely track & 'cruise'.  For the track, the silencer will have a small side pipe much like Dax's design.  This is very efficient, but not very passenger friendly on any longer journeys than 10 minutes.  For this reason I want to also make the car have the option (through a spring tightened slip on system) of a rear exit pipe.