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Pulling a depression (vacume) in the crankcase does have a positive effect on FE and power production. Poor boy dyno test jack up rear wheels. (RWD of course) start engine transmission in high gear set throttle for 3,000 rpm. crankcase at atmospheric pressure. Pull 8" hg vacume into crancase. RPM gain about 50 RPM. (small but measurable) aerodynamic drag on crankshaft is reduced. Shape leading and trailing edge of counter weight of crankshaft into the shape of an airfoil for further gains. Pulling more then 8" will produce more gain but will exceed the design limitations of seals and gaskets.
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