equation to compute compression ratio

[UnderDog]

I am trying to figure out what the formula for computing the compression ratio on a car is. Does anyone even know what i am talking about and if so where i could get this at?

[cupcake]

((((3.14*(Bore/2)^2)*(Stroke+Thickness of headgasket))+Combustion chamber volume)/(Combustion chamber volume+((3.14*(Bore/2)^2)*thickness of headgasket))=compression ratio

This equation works for a flat top piston with no fly cuts, dishes, or pop-ups. If you have any of these you need to add or subtract volumes according to initial and final volumes.

[spastik]

wow, nice cupcake!

[InSepsis]

props for the skills.

[UnderDog]

((((3.14*(Bore/2)^2)*(Stroke+Thickness of headgasket))+Combustion chamber volume)/(Combustion chamber volume+((3.14*(Bore/2)^2)*thickness of headgasket))=compression ratio

This equation works for a flat top piston with no fly cuts, dishes, or pop-ups. If you have any of these you need to add or subtract volumes according to initial and final volumes.

what do all the (((*^ mean?

[cupcake]

() = do whats inside first, ie (3*(4+5))=(3*(9))=(3*9)=27
* = multiply
^ = raise to the power of, ie 3^2 = 9, 3^3 = 27

Or how about, what is the bore, stroke, combustion chamber volume, and what type of piston do you have?

[spastik]

The Distributive Property is an algebra property which is used to multiply a single term and two or more terms inside a set of parentheses. Take a look at the problem below.
2(3 + 6) Because the binomial "3 + 6" is in a set of parentheses, when following the Order of Operations, you must first find the answer of 3 + 6, then multiply it by 2. This gives an answer of 18.
2(3 + 6)
2(9)
18

[82z28]

http://kb-silvolite.com/calc.php?action=comp

[racerX 244]

this was the first result that popped up in google for "compression ratio formula."

http://www.greatplainsas.com/icompratio.html

Step by step process:

1. Determine the displacement of your engine. Displacement formula is:

BORE X BORE X STROKE X .0031416 = DISPLACEMENT

Example: 92 x 92 x 82 x .0031416 = 2180cc

2. Determine the swept volume of one cylinder:

Example: 2180cc divided by 4 = 545cc

3. Determine the deck volume of each cylinder. The deck volume is the distance from the top center of the piston to the top of the cylinder when the piston is at top dead center. Measurement is made in thousandths.

Example: on cylinder #1 you measure and find you have .020" deck height.

BORE X BORE X DECK HEIGHT X .01996 = CC"s

Example: 92 x 92 x .020" x .01996 = 3.378cc's

Measure each cylinder.

4. Measure the volume in each cylinder head. To do this, use a piece of plexiglass cut to fit in the cylinder head to cylinder mating area. Drill a 1/4" hole in the center of the plexiglass. Lightly grease the edge of the plexiglass and install in the head. (Spark plug and valves have to be installed) with a syringe graduated in cc's fill the cylinder head chamber up with a light weight oil. Record the measurements. Repeat for other three chambers. Average cc volume of a new head chamber is between 47 and 51 cc's.

5. You now have all the measurements to determine your compression ratio.

one cylinder swept volume + deck cc + head cc

deck cc + head cc

Example: 545 + 3.378 + 48 = 596.378

3.378 + 48 = 51.378 = 11.6:1

In this example, 11.6:1 is the actual unadjusted compression ratio for one cylinder. Add cylinder shim thickness which will increase the deck cc volume and refigure compression ratio. This must be done for all cylinders. Average deck height shim for use on a 2180cc engine will be between .150" and .185". We use a .177" shim for AVGAS and a .216" or .256" shim for unleaded premium auto fuel. Lower is better for increased engine life and fewer valve related problems.

[UnderDog]

word, thanks guys! And now to take the measurements..