Miata Mailing List: September 1998, Message #21

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In a message dated 98-08-31 21:54:17 EDT, k.summers@mail.utexas.edu writes:

<< 
 I am a little curious as to how I might compare compression and boost.  It
 seems to me that both performance options can achieve similar results, but
 there are a few things that have me confused. 
 1.  is there a correlation between higher units of compression and boost?
 i.e. can one say, for instance, raising the compression ratio from 9.4:1 to
 10.4:1 achieves the same performance increase as running a given p.s.i. of
 boost?
 2.  I have always heard that running very high compression requires the use
 of high test gas (higher octane than pump gas).  Is this necessarily true
 if one uses a programmable computer to maintain a proper A/F ratio?
 3.  Why have I heard that relatively high compression (upwards of 11:1) is
 not a streetable option, especially if people regularly run 1 bar of boost?
  It seems to me that the concepts are fairly similar.
  >>
Hi Kurt,
Long story, high points.
Any engine make power by moving air and fuel through it.  Bigger, more air.
More rpm, more air.  The compression ratio only affects the efficiency with
which power is taken out of the air/fuel mixture.  

Typically, a point on CR is worth about 4 to 5% in power.  A psi, although a
decreasing function,  nets between 6 an 10 %

The heat induced by any process is the basic cause of knock. Compression makes
heat, boost makes heat. Octane resists knock.
Regards,
Corky