I think larger inlet ports might be due to the fact that more gas, by
weight, is entering the chamber under lower absolute pressure, whilst the
exhaust ports have to handle less total weight of gas under higher absolute
pressure.
Inlet is assisted by piston downstroke and exhaust the opposite, so the
mechanical effect is nearly the same, with the volumetric change. There is the
pressure drop through the 'inlet' and 'outlet' piping, which should have been
designed into the engine performance characteristics.
There is more gas by weight (fuel and air) going into the chamber which
would require larger 'pipe size' than exiting (much less fuel and somewhat
less Oxygen plus some combustion by-products) requiring smaller pipe size.
Most 'pumps' which convert one form of energy into another have larger
inlets than outlets (if normally aspirated; some jets and plasma engines, as
well as forced fuel entry is another animal).
Regards,
CB
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