way to find compression ratio?
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From: MN
way to find compression ratio?
is there any real test to find the compression ratio on a car? i have 9.1 to 1 pistons in and my compression test shows a solid 150 across the board, it just seems alittle low to me, with a stock head gasket
Joined: Sep 2004
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From: amherst, ny, US
Re: way to find compression ratio? (Btothe3rdDegree)
well your running semi low compression pistons, whos the manufacturer of teh pistons call them up and ask what a projected compression would be for your set up im sure they would have a set standard. are you running a stock head/valve train?
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From: IN STORES NOW
Re: way to find compression ratio? (Btothe3rdDegree)
the static compression ratio is found by the cubic volume of the cylinder at BDC and divide that by the clearence volume TDC. for example if the cylinder measures 100cc at BDC and at TDC it equals 10cc then your static compression ratio would be 10:1 
to perform this properly you will need a dial indicator and some sorts or a jig to hold firmly in place as the crank is rotated. the cheap way...take a small rod like your dip stick. with the spark plugs removed insert the dip stick into the chamber throught the spark plug well and have some one rotate the crank untill it stops moving (at this point you have half a crank before it starts the compression stroke. mark the dipstick in relation to the top of the valve cover and do the same for the compression stroke, marking it as well. then measure the distance from the first mark to the end of the dip stick (the end being what was sitting on the piston top). that measurement being your total volume, then measure the distance between both marks, divide the two numbers and that will give you a rough estimate of your static compression ratio. remember measure in centemeters. this by far an accurate measuring method but it will roughly give you a ratio.
to perform this properly you will need a dial indicator and some sorts or a jig to hold firmly in place as the crank is rotated. the cheap way...take a small rod like your dip stick. with the spark plugs removed insert the dip stick into the chamber throught the spark plug well and have some one rotate the crank untill it stops moving (at this point you have half a crank before it starts the compression stroke. mark the dipstick in relation to the top of the valve cover and do the same for the compression stroke, marking it as well. then measure the distance from the first mark to the end of the dip stick (the end being what was sitting on the piston top). that measurement being your total volume, then measure the distance between both marks, divide the two numbers and that will give you a rough estimate of your static compression ratio. remember measure in centemeters. this by far an accurate measuring method but it will roughly give you a ratio.
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From: IN STORES NOW
Re: way to find compression ratio? (liquidxEG)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by liquidxEG »</TD></TR><TR><TD CLASS="quote">couldn't you just do a compression test and check the #'s?</TD></TR></TABLE>
he asked for a way to figure out compression ratio...not compression.
compression just shows how many psi the cylinder can produce not how much it could hold (volume) you need both to figure out a ratio. thats why I recommend the back woods method of attaining the static ratio.
he asked for a way to figure out compression ratio...not compression.
compression just shows how many psi the cylinder can produce not how much it could hold (volume) you need both to figure out a ratio. thats why I recommend the back woods method of attaining the static ratio.
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