Re: Compression questions

[mousetrap@juno.com]

>>What excactly do the numbers mean though, does the "1" represent the
>>lowest point of the piston and "8.5" (for example) represent the
>>highest point.  Do they represent distences or pressures? therefor
>>the 1 would be the bottom of the stoke (no pressure) and the "8.5"
>>represent the amount of pressure at the top of the stroke?  If so,
>>what messurement are the numbers in, psi?

>
>Well, basically, a 10:1 engine is taking 10 units of air/fuel and
>compressing it into the space one unit occupies, hence the phrase "Ten 
>to
>one."  Basically.  It is not possible, really, to extrapolate a pounds 
>per
>square inch value from a compression ratio.  Compression ratios are
>determined by bore and stroke vs. combustion chamber.  B&S determines
>volume, the amount of air/fuel, like a can of beer - if you took the 
>bore
>and stroke, or the diameter and height of a beer can, you could figure 
>out
>mathematically how much air is inside the can.  This is basically what 
>bore
>and stroke tells you, among other things.  Then, the volume of the
>combustion chamber, where all the unburnt gases are stuffed 
>pre-ignition,
>is the other side of the equation.  The piston moves downward, sucking 
>in
>air/fuel, then back up, compressing it into the CC - 10 units of air 
>into
>the space of 1.  Basically.  So, to corrolate the CR with PSI is 
>impossible
>- an 8.5:1 engine is always 8.5:1, no matter how well the valves/seals 
>are
>holding the pressure.  8.5:1 is a mathematical figure, whereas the
>PSI/compression test is a physical test - the engine is still taking 
>in 8.5
>units of air/fuel, still putting that air/fuel into the CC, but it 
>does not
>know if the a/f is rushing out past a burnt, cracked exhaust valve, or
>leaking out past a ring.  Hope this makes sense, it is one of those 
>things
>I simply understand, but have never tried to put into words, although 
>I
>think I got it (basically) right & comprehendable.
>
>
>Mannix(there's WAY more to it than that, but the basic jist is there)

Well put.
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