Yep that is interesting. I think it has to do with the pressure

difference.

     Exhaust gas has a greater pressure difference behind it.
     Also there is limited room for poppet valves in a piston engine so

larger

     intake valves at the expense of the exhaust valves generate more

power.

     Paul Lamar

Paul, My assumption has always been there is less to exhaust than to

take in. Since the fuel air mix it combusted to provide the power, the
by-products are less ( in volume) than the intake charge.

Bill Jepson

Bill - There is definately more volume  in the exhaust than in the intake
charge,
primarily because it is hotter. In the four stroke it is pumped out, in
addition
to having pressure because it has not been totally expanded. The residual
weight
at exh tdc is less because of the temp so this residual  is less of a factor
than
the ability to fully charge on intake. On poppet valves it is also tempting
to make them smaller because they are the easier to cool. Obviously the
weight
flow out has to be equal to the wt flow in (except for blowby and other
destructive leakage).
Vance

 
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