back pressure is but one factor which accounts for the
efficiency of the exhaust system. which as the name implies,
operates as a system. meaning, no single component accounts for the
factor "back pressure" on its own.
sure, more free flow pipe and muffler = lesser back pressure is
great for power production, but having unequal extractors does have
its drawbacks on how efficient these items work in tandem as one
entire system.
imagine (i know nothing happens perfectly and as slowly in real
life) each cylinder produces x cm3 of exhaust in a single exhaust
stroke. it may take extractor primary 1 twice as long to transfer x
amount of exhaust to the downpipe than extractor primary 4 which is
shorter. while this is happening, the 2nd and 3rd and so forth
exhaust strokes are creating 3x, 4x..... "clogging" up primary 1
compared the exhaust in primary 4 which may have already reached
the down pipe.
multiply the effect in an engine typically operating in the range
of 1k-6k rpms, u have pretty chaotic situation there.
