Simple Definition of Compression
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Simple Definition of Compression
In the most basic terms, it is the difference of the volume in the cylinder/combustion chamber at the bottom of the stroke VS the top of the stroke. So a 10:1 would mean the volume at TDC is one, and the volume at BDC equals ten times the volume at TDC.
Bill
1999 neon coupe 2.4 swap
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2000 Neon MTX swap with '02 R/T PCMOlha Koba, a psychologist in Kyiv, said that “anger and hate in this situation is a normal reaction and important to validate.” But it is important to channel it into something useful, she said, such as making incendiary bombs out of empty bottles.
1999 neon coupe 2.4 swap
2021 Forester
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and for more clarification just in case...
TDC = Top Dead Center, when the piston is as far up in the block as it will go.
BDC = Bottom Dead Center, when the piston is as far down in the block as it will go.
TDC = Top Dead Center, when the piston is as far up in the block as it will go.
BDC = Bottom Dead Center, when the piston is as far down in the block as it will go.
-Frank
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- Swordfish2Cowboy
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I got a Sticky!
Bill
1999 neon coupe 2.4 swap
2021 Forester
2000 Neon MTX swap with '02 R/T PCMOlha Koba, a psychologist in Kyiv, said that “anger and hate in this situation is a normal reaction and important to validate.” But it is important to channel it into something useful, she said, such as making incendiary bombs out of empty bottles.
1999 neon coupe 2.4 swap
2021 Forester
- fixitmattman
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How is this a sticky?
http://www.cardomain.com/profile/fixitmattman
How to fix your car:
1. Buy a Haynes manual
2. Read Haynes maual
3. Read and search appropriate threads, trust us, it's been covered before
4. Fix car
5. Consume beer of job well done
How to fix your car:
1. Buy a Haynes manual
2. Read Haynes maual
3. Read and search appropriate threads, trust us, it's been covered before
4. Fix car
5. Consume beer of job well done
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Someone asked, so I made it so. Why not
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A litle more detail, since it has been stickied, may as well do it right.
Second Chance Garage:
Second Chance Garage:
There are plenty of sites that go into detail, just search for "How to calculate compression ratio.Calculating Compression Ratios
Just because your engine was manufactured to have a certain compression ratio doesn't mean its true "as-assembled" ratio is close to that specification. This is very important, since ignition timing, fuel delivery and overall performance are directly related to an engine's compression ratio.
Many engine components must be set up and optimized to the compression ratio, so knowing exactly what that number is becomes a critical measurement, especially in situations where different heads, valves, camshafts and other internal parts have been changed.
So how is it done? Actually, it's quite easy but first we need to define some terms:
Bore: The diameter of each cylinder expressed in inches.
Stroke: The length of travel of the rod/piston. Note: you can use the manufacturer's specification for this value, but if a different crankshaft with a non-stock "throw" is used or different rods and pistons are used, the stroke must be measured.
Combustion Chamber Volume: This is the total volume, in cubic centimeters, of each combustion chamber (the depression in the head surface that contains the valves and spark plug.) To obtain the volume, place the head level and inverted on the bench, with its valves and plug(s) installed. Fill each chamber with alcohol or mineral spirits from a measured container or syringe until the chamber is full and surface tension keeps the fluid from running out. Note the exact amount for each combustion chamber and add up the totals, converting any measurement to cubic centimeters. Note: 1 cubic centimeter = .061 cubic inch. To convert ounces to cubic centimeters, divide the cc number by 29.57
Deck Height Volume: This is the area of bore between the top of the piston and the top surface of the block when the piston is at the very top of its stroke. The formula for calculating this value is: bore x bore x .7854 x measured deck height.
Head Gasket Volume: The head gasket takes up space and is therefore part of the cylinder's overall volume. To calculate the head gasket's volume, use the formula: bore x bore x .7854 x compressed gasket thickness.
Swept Volume: The swept volume is the displacement of one cylinder as calculated by the formula: bore x bore x stroke x.7854
Constant Volume: The constant volume is the volume into which the swept volume is compressed on each compression stroke. This value includes the combustion chamber volume, head gasket volume and deck-height volume.
Once all these values are measured and calculated, we can accurately calculate the compression ratio of this specific engine. The formula for computing compression ratio is:
CR= Swept volume + Deck Height volume + Head gasket Volume + Combustion Chamber volume
--------------------------------------------------------------------------------
Deck height Volume + Head Gasket Volume + Combustion Chamber Volume
Of course, there are situations where everything isn't this simple. This formula only applies to "flat-top" pistons and not domed or dished pistons. Even flat-top pistons have little cuts in them for valve clearance, called "valve relief."
Not to worry, however. For domed pistons the manufacturers provide the values that these pistons reduce the combustion chamber volumes, so just do the arithmetic. For dished pistons or valve reliefs, use the syringe method to measure the additional volumes and add to the combustion chamber volume.
Bill
1999 neon coupe 2.4 swap
2021 Forester
2000 Neon MTX swap with '02 R/T PCMOlha Koba, a psychologist in Kyiv, said that “anger and hate in this situation is a normal reaction and important to validate.” But it is important to channel it into something useful, she said, such as making incendiary bombs out of empty bottles.
1999 neon coupe 2.4 swap
2021 Forester
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Bill
1999 neon coupe 2.4 swap
2021 Forester
2000 Neon MTX swap with '02 R/T PCMOlha Koba, a psychologist in Kyiv, said that “anger and hate in this situation is a normal reaction and important to validate.” But it is important to channel it into something useful, she said, such as making incendiary bombs out of empty bottles.
1999 neon coupe 2.4 swap
2021 Forester
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- jonnymopar
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Or your spine when you give them piggyback rides.
Ooooo, somehow that seems wrong, piggyback rides, and fat chicks in the same thread.
Bill
1999 neon coupe 2.4 swap
2021 Forester
2000 Neon MTX swap with '02 R/T PCMOlha Koba, a psychologist in Kyiv, said that “anger and hate in this situation is a normal reaction and important to validate.” But it is important to channel it into something useful, she said, such as making incendiary bombs out of empty bottles.
1999 neon coupe 2.4 swap
2021 Forester
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Well the 2003 to 2005 non magnum 2.0's are 9.3:1
The older ones are all 9.8:1.
That is 9 and 3 tenths of a compression point. That is what the "3" means, if I understand your question properly.
FWIW, the FSM list them at 9.4 tho. Just what the actual non rounded off figure is, IDK.
The older ones are all 9.8:1.
That is 9 and 3 tenths of a compression point. That is what the "3" means, if I understand your question properly.
FWIW, the FSM list them at 9.4 tho. Just what the actual non rounded off figure is, IDK.
Bill
1999 neon coupe 2.4 swap
2021 Forester
2000 Neon MTX swap with '02 R/T PCMOlha Koba, a psychologist in Kyiv, said that “anger and hate in this situation is a normal reaction and important to validate.” But it is important to channel it into something useful, she said, such as making incendiary bombs out of empty bottles.
1999 neon coupe 2.4 swap
2021 Forester