> And while we are at it, here's one that fails freshman algebra:
> if I have a 9:1 compression ratio engine should i expect an
> combustion chamber pressure of 9 x ambient pressure. i don't
> think so as 9 x 14 = 126 psi. i measure (to specs) 180 psi!
> what am i missing here?
What you're missing is the fact that rather than an isothermal compression,
you're getting something in between isothermal and adiabatic (that is, the
temperature of the charge increases during compression). The formula for
ideal adiabatic compression is P2 = P1(V1/V2)^lambda, where lambda is
about 1.4, giving about 289 psi. The difference between this value and what you
do get is accounted for by heat transfer between the charge and the cylinder,
piston, head, valves, plug, etc, plus any blow-by.
John R. Lupien