I thought that a simple ratio of compressed volume to
uncompressed volume will not give the actual ratio as there are
"pumping" factors to consider: so says "Mark's Standard Handbook
for Mechanical Engineers."
"The nominal compression ratio (usually specified) is the
displacement plus clearance volume divided by the clearance
volume. The actual compression ratio is appreciably less than
the nominal value because of late intake valve or port closing."
"The compression pressure may be estimated from the relation P= r
to the power of 1.33 times p where p is the intake-manifold
pressure and r is the actual compression ratio."
Blake
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