In simple terms the Static Compression Ratio is with the piston at Bottom Dead Center (BDC) or full stroke, it's all the volumes under and including the combustion chamber to the piston crown and including any volumes created by the shape of that crown divided by the volumes under and including the combustion chamber and piston crown with the piston at Top Dead Center (TDC) all the stroke used up.
To get to the total volume calculates the following then add them together:
1) The swept volume of the cylinder simply the stroke times the formula for the area of the piston/bore diameter.
2) The clearance volume measured from the outer edge of the piston diameter to the top of the block called the deck, or head deck.
3) The volume of the piston crown, flat tops add nothing except a small amount for valve clearance reliefs present, dishes add volume, and domes subtract volumes. One can include what’s called the crevice volume from the very edge of the piston diameter to the top ring, but given it's pretty consistent unless you're anal about numbers it's usually ignored.
4) The volume of the head gasket which can be thought of as bore area based on gasket bore diameter times the thickness of the gasket. Note that gaskets usually aren't exactly round but if you don't have the manufacturer's volume or your calculus skills for areas of weird shapes are rusty; area of the round bore times thickness of the gasket is plenty close enough.
5) Last is the volume of the combustion chamber itself. If you can't measure it directly you're stuck with the manufacturer's stated volume. This is usually small compared to real volume and of course the actual volume will vary is the head has been milled reducing volume as a result; and or a valve job (has been performed) which sinks the valves deeper which adds volume back.
Adding 1 through 5 gives total cylinder volume. Adding 2 through 5 gives the volume into which all the volumes are compressed at TDC. Dividing the sum of 1 thru 5 by the sum of 2 thru 5 gives the Static Compression Ratio or (SCR) Where this gets complicated is when the engine is assembled and you have to make some assumptions about what's inside.
You also need to switch back and forth between English and metric measurements for cubic inches and cubic centimeters. There are 25.4 millimeters to the inch and 16.4 cubic centimeters to the cubic inch, from those we can hack what we need.
So let's peel this baby apart with reference to the process listed above.
1) A 350 uses 3.48 inch stroke and 4 inch bore. The long way around to the bore area is 1/2 diameter squared times pi (3.1416). So half of 4 is 2 times itself which happens to be 4 again, times pi which nets 12.5664 square inches of bore area. This times the 3.48 inch stroke is 43.7310 cubic inches. That times 8 equals 349.8486 cubic inches which Chevy rounds to 350. We can use the cylinder volume in cubic centimeters later so 43.7310 times 16.4 cc's to the cubic inch makes 717.1884, I'll round that to 717.2 ccs to reduce the math load.
2) The GM states the Clearance Volume from piston crown to head deck is .025 inch that times the bore area of 12.6 sq inches (rounding) equals .315 cubic inch which times 16.4 cc/in is 5.166 cubic centimeter.
3) Here's something you've got to guess at as GM uses several different pistons with round dishes of different volumes but a pretty common one is 13 ccs so we'll grab that. There's bigger!
4) Head gasket volume, well the bore of these is larger than the bore's diameter; a 4.1 inch gasket bore on a 350 is pretty common. We also have to guess at the factory gasket thickness, these range from about .020 inch for a shim to .053 for a composite. Most trucks came with the shim. If we use the same formula as figured for the bore the larger 4.1 inch gasket generates an area of 13.203 square inches times a thickness of .020 equals .264 cubic inches times 16.4 equals 4.33 cubic centimeters.
5) Combustion chamber well since it's on the motor we'll have to take the factory at its word and use 75 ccs.
So if we add 1 through 5 for cubic centimeters we get 814.69 (rounding as I go). Adding lines 2 thru 5 gets 97.5. Dividing 814.69 by 97.5 results in a compression ratio of 8.355 to 1. That's the process to get to the Static Compression ratio (SCR). In reality having measure more than a few of these engines the dimensions not including the bore and stroke but especially of the combustion chamber tend to be a bit larger than published. You find the actual measured SCR runs more like 7.6 to 7.8 rather than in this case the calculated 8.355 which is very close to GM's advertised ratio.
I've given you enough ammo to compute the 64 cc head compression for yourself, it will go up. Raising the compression is something the 279T cam will need to get all it has. This gets into the field of the Dynamic Compression Ratio or (DCR). The DCR adjusts downward the SCR for that point where the cam closes the intake valve in crankshaft degrees. The arithmetic for this most defiantly gets into trigonometry but there are a lot of DCR calculators on the web to make life simpler. You'll need the rod length which for the 350 is 5.7 inches. You'll need the cam card to get when the intake gets seated in crank degrees. When you get that data here's a place to go play with numbers <<<
http://www.kb-silvolite.com/calc.php?action=comp2 >>>. You want to calculate an SCR that provides a DCR pretty close to 8 to 1.
I've got to go for awhile, have fun.
Bogie