At 12:05 AM 3/27/98 -0700, Mark Bradakis wrote:
>There is a formula that does come close, involving a number of terms, a few
>powers of this and that, a logarithm or two, but it is still only an
>approximation. And of course, I can't dig it up at the moment, it was around
>here somewhere...
Mark is correct, here is the formula.
Compression Ratio = (C - P + G + D + V) / (C - P + G + D)
C = combustion chamber volume
P = piston dome volume
G = head gasket volume
D = deck height volume
V = cylinder block volume
I just asked this very question from a friend of mine an he sent me the
above formula ( I have no clue how to apply this formula!). Basically it
says the combustion ratio is the relationship of the volume of the entire
combustion chamber (head and cylinder) when the piston is at the bottom
dead center, to the volume of the entire combustion chamber when the piston
is at top dead center.
A compression tester cannot determine compression ratio. The compression
ratio the a ratio of the physical properties of an engine and does not
change, regardless of the condition of the engine. Compression on the
other hand is a reflection of the condition of the engine and can change
over time. As compression goes down, the compression ratio doesn't change.
Larry Hoy Denver CO USA
1969 MGB
1987 Jaguar XJ6 VDP
"It's not how fast you go it's how fast you go fast"
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