The exhaust manifold system should be as small as possible in terms
of pipe length and bores. The shorter the pipe length, the less likelihood
there is of pulse reflections occurring during the scavenge period.
The smaller the pipe bore, the greater the preservation of exhaustpulse energy, though too small a bore may increase the frictional
losses of the high velocity exhaust gas to more than offset the increased
pulse energy. Sharp bends or sudden changes in pipe cross-sectional
area should be avoided wherever possible.