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I learned this from a mechanic.
4 cyls have no overlap, exhaust has to be precise for homogeny. That is many times a locale, the common fuel, turbo, no turbo, carbed, injected, low compression, high compression, big volt ignition, low volt, single fire , double fire, and how much air from idle to full throttle?
and then you know what I learned..the same exact exhaust can be swapped through all engines, because there is no two cylinders firing at the same time.
in the 8 cylinder world, and beyond, there is 90 degree overlaps, then in the 10 cyl it is 72 degrees, the 12 it is 60.. if you are running deep, there is reasons, very rare, to have what look like stove pipes, like a diesel...
other than that, it is trial and error. even ignition strength alters what is needed. The length of the exhaust sytem may call for something else..my own is 1781cc, with a 2.25 axle back, on a carbed engine...sounds bizarre, until mentioning 14.6 feet to get to the back..the little pipes it could use, are bad because of it.
and that brings how much heat is sustained, are pipes covered? going by a spinning driveshaft drops temps..fwd does not have to worry of this..etc etc etc etc
there is a precision after all.
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