volvo compression test

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rubberduck

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Does anyone know what a good result is from a compression test on a 1983 Volvo AQ125A?

I'm planning on testing it this weekend but don't know what range I should be in.

Thanks
 

Starflight

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Re: volvo compression test

The book calls for 9.3:1 compression ratio and between 146-174 psi.
 

bruceb58

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Re: volvo compression test

FWIW...it is more than 136psi.

You can't calculate the pressure just by the change in volume. You have to take into account energy introduced. This also increases the pressure.
 

Dunaruna

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Re: volvo compression test

[colour=blue]
Limited-Time said:
FWIW 9.3:1 compression = 136 psi

In a perfect world - yes. But there are way to many variables to nail down an exact correlation.

Rubberduck, taking into account the age, a good result would be around 140-150 with no more than 5% variation.
 

bruceb58

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Re: volvo compression test

Curious how you think 136 PSI in a perfect world.
 

Dunaruna

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Re: volvo compression test

[colour=blue]14.7 x 9.3 = 136.71.

Maybe I should have said 'theoretical' world.
 

Limited-Time

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Re: volvo compression test

bruceb58 said:
Curious how you think 136 PSI in a perfect world.

Atmospheric pressure = 14.695 PSI,(at sea level) 14.7 X 9.3= 136.6 PSI
 

bruceb58

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Re: volvo compression test

Pressure(initial) = Pressure(ATM) + pressure(gauge) = 14.7 PSI. In this case, pressure(gauge) = 0 PSI

pressure(final) = pressure(ATM) + pressure(gauge) = 136 PSI. Since pressure final = 136, pressure gauge = 136-14.7 = 121.3 PSI.

Of course the presure final will be way higher that this because the temperature is not constant. By compressing the air, a lot of energy was introduced by the work necessary to compress the air. This causes the temperature to rise drastically and hence causes the pressure to rise.

This phenomenon is what cause air conditioning to work. Ever feel the output of a compressor? Pretty hot!

I can see how you guys thought it was 136. You were assuming Ideal Gas Law but forgot about temperature rise and how pressure(gauge) works.
 

Don S

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Re: volvo compression test

That's why the dreaded SERVICE MANUAL that most people seem to really hate to own, says 146-174 psi.
 

bruceb58

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Re: volvo compression test

yeah...I bet the Clymer manual says 136.
 

Don S

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Re: volvo compression test

More likely it says 631 :devil:
 

Dunaruna

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Re: volvo compression test

[colour=blue]I didn't say it was 136.

If you read the posts - we all agree. But it seems we must have a maths lesson from Bruce and a shot across the bow from Don to end the thread.
 

bruceb58

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Re: volvo compression test

it wasn't a math lesson...it was a thermodynamics/chemistry lesson!

I just wanted people to realize you cant just multiply the atmospheric pressure times the compression ratio to get the pressure.
 

Tail_Gunner

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Re: volvo compression test

My money is on Don he's rarely wrong no offense guys..........
prod.gif
 

erock35

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Re: volvo compression test

WOW!! Put on your gloves and get in the ring. This could be a draw!!:confused:
 

Bondo

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Re: volvo compression test

it wasn't a math lesson...it was a thermodynamics/chemistry lesson!

Ayuh,... Good Thing,... 'cause I ain't no Mathamagician.....
But,...
I am a Mechanic...

If I had a 9.3:1 motor showing 136psi,... I'd be comtemplating a Tear-down,+ Rebuild....
 

bruceb58

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Re: volvo compression test

Bondo,

You got bit by the old 4 year old thread again!
 

Bondo

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Re: volvo compression test

Damn,......:rolleyes:

I thought this was abit Exciting, considering I only left the keyboard long enough to go buy groceries....
 
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