There are 2 ball joints in my Renesis exhaust system (before the collector) and a very short  piece of flex pipe between the exhaust collector and the muffler.  The ball joints were for ease of building as much as for vibration protection. 

 

My system is not the optimum for max power but it fits the airplane, is reasonably quiet and does not crack.  It makes 200 HP which is pretty sporty in an airplane but a car racer wouldn't bother taking it to the track that way.

 

Tracy