The other part of the equation is that whenever a gas is compressed it is
also heated, and if that heat is not completely dissipated it will, in turn,
contribute to a further increase in pressure beyond the pressure achieved by
mechanical means.
-----Original Message-----
From: Dan Buettner <danb@thelittlemacshop.com>
To: triumphs@autox.team.net <triumphs@autox.team.net>
Date: Tuesday, February 22, 2000 11:56 PM
Subject: Re: 76 tr6 compression
>
>>Rod MacLeod wrote:
>>
>> > Can anyone tell me the proper compression in pounds per square inch
for a
>> > healthy 1976 carburater model tr6. All I ever see is a ratio (7.75 :1)
and
>> > I'm no math jeanie ass.
>>
>>Can it be as easy as multiplying atmospheric pressure (14.7 psi) times
>>compression ratio? For 7.75 that would be 114 psi. That sounds low but
so
>>does 7.75.
>>
>>I assume that whatever the formula is it will vary based on your altitude.
>>
>>Geo Hahn
>>59 TR3A
>>Tucson, AZ
>
>You're right, Geo ... with a small "but". You also have to consider
>what's called 'volumetric efficiency', i.e. the ability (or
>inability) of the internal combustion engine to completely fill the
>combustion chamber with the air-fuel mixture during the intake stroke.
>
>Now, I'm recalling from a long-ago memory of reading a couple of
>books on turbocharging, so my number may be off, but I believe that a
>"normally aspirated" engine (not supercharged or turbocharged) works
>at about 85% volumetric efficiency.
>
>Basically, the engine just can't quite fill itself up in the short
>time the intake valves are open due to the flow restrictions of the
>air filter, carbs, manifold, etc.
>
>That being said, my Bentley manual quotes 8.5:1 for the compression
>ratio on my TR3 and also quotes 120 psi as the compression pressure.
>If you do the math, those numbers would indicate 96% volumetric
>efficiency based on 14.7 psi atmospheric pressure. (so maybe I'm
>full of it)
>
>What's more important than the "correct" reading is consistency of
>the readings across all your cylinders. Readings much higher or
>lower than the rest may indicate carbon build-up, broken rings, etc.
>I've heard from some folks that you should be concerned if your
>readings are more then 10% different between cylinders; others say 10
>lbs.
>
>Hope this is helpful and that I'm not just babbling!
>
>Dan
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