The calculations for supercharging

["John Fielding" <johnf@domain.elided>]

Hi All,

Lets put his argument to bed!

Assume a 1 litre motor.  It will ingest 1 litre of air for every two revolutions of the
crankshaft (neglecting the small pumping losses inherent in all piston motors) so at 3000
rpm it ingests 50 litres per second.  At 6000 rpm it will therefore ingest 100 litres per
second.

1 litre is 61.02 cu. inches.  So our motor turning at 3000 rpm will ingest 3051 cu. inches
per second, or approx. 183060 cu. inches per minute.  There are 1728 cu. inches in a cu.
ft, therefore the motor ingests 105.93 cfm.  At 6000 rpm  - assuming the same pumping
efficiency - the motor ingests twice this amount of air = 211.8 cfm.

From tables for typical air compressors using vane blades:  An electrical  blower with a
100 cfm throughput at 0.7 inches of water  (0.025 psi) requires approx. 75 watts.

There are 12 inches of water per foot. 1 psi = 2.307 ft water, 1 BAR of boost is equal to
14.5 psi or 33.45 ft water gauge.

Therefore to develop 1 BAR of boost with a 100 cfm throughput requires: 43.5kW = 58.3 HP

Someone please check my calculations!

John
Durban
South Africa
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