hpras wrote:Exhaust is small because only one cylinder fires at a time, and the final exhaust pipe can be seen as an extension of the header pipe. Having the final exhaust small helps keep the exhaust velocity up which helps scavenge the next exhaust pulse.
but ...2 exhaust valves are opened at the same time ,if not both fully but still.. so
this is the reason why a 1 cylinder engine is not producing 1/4 of the power of a 4 cylinder.. scavenging and cylinderfilling is helped by this potentially..
My guess would be the smaller the diameter the less pulsing you will get in the exhaust stream ? the exhaust pipe is not very long either..and maybe it is also a bit of a perspective thing of the picture..