Joseph R Schneider wrote:
> ... anyway, given typical
> compression ratios in the 8:1-10.5:1 range and atmospheric pressure of
> 14.7psi (760 torr, average at sea level), and neglecting adjustments for
> compression of gas at constant energy (tends to increase temperature and,
> therefore, pressure in the compression chamber during compression stroke)
> and the fact that intake is not totally efficient and also that intake
> valve usually still partially open as the compression stroke starts, you
> should expect cylinder compression to be about 14.7*(8.0-10.5), or
> 120-160psi...
I don't know why I've never realized that the compression check provides an
"experimental analysis" of the compression ratio. This makes sense to me.
It seems that people are often asking what the "normal" values are for the
compression check on their car -- the above simple calculation would give a
good ballpark figure.
Thus, for the TR6:
ratio check psi
pre '72 8.5:1 125
'72-'76 7.75:1 114
Is there something else that is missing from the above? Are the other
adjustments that Joe mentions significant, or down in the range of errors
inherent in the compression test itself? (say, less than 10%?)
The above numbers are consistent with my sample size of compression tests
(1), since when I did a compression test on my car, a '74 TR6, I found
numbers that ran from 110psi - 128psi.
--ken
Kenneth B. Streeter | EMAIL: streeter@sanders.com
Sanders, PTP2-A001 |
PO Box 868 | Voice: (603) 885-9604
Nashua, NH 03061 | Fax: (603) 885-0631
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