The compression test result measures static compression. The actual dynamic
compression ratio is probably not as high as all that (in any single stroke,
considering valve timing). Dividing by 14.7 is not really a meaningful
calculation. Think about it -- many vehicles will return a result of more
than 147psi -- but few vehicles have a nominal compression ratio of 10:1 or
higher.
That said, the 195 figure does seem somewhat high -- one wonders if the
exhaust valve is opening.
--
Max Heim
'66 MGB GHN3L76149
If you're near Mountain View, CA,
it's the primer red one with chrome wires
on 10/11/06 6:47 PM, bill at bilking@comcast.net wrote:
> 13:1 compression in #3. I assume the other 3 were similar in the past.
> Where did you get fuel for such a beast? Bentley defines high
> compression as around 11:1. Do you know how much they took off when
> they decked the head? I'd put 2 head gaskets at a minimum if I owned
> this engine.
>
> And before you all go off- if you take the pressure indicated on the
> compression tester and divide it by 14.7 which is atmospheric pressure
> you have actual compression ratio. If you take volume at bdc and divide
> it by volume at tdc you get a theoretical compression ratio which
> doesn't take into account leakage around rings and valves (or through a
> blown head gasket). I'd expect the theoretical compression ration would
> be higher than 13:1. It all goes back to PV=nRT.
>
> Bill
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