Alright, I know this is probably basic knowledge for most guys on here, but it seems to elude me. Now I will use my own engine as an example, and remember, I am just trying to figure out how this all relates to each other. Here goes:
Summit sells engine kits for a 454 all together that I was reading about and noticed all their stated compression ratios are at .030 over. So lets just say I pick a piston that says 10.37 CR with 116.9 cc chambers, everything else the same where does the CR go if I were to bore .060. I guess it goes down, but how far? This is just hypothetical to help me understand the relationship of things although the stated engine kit is directly from the catalog, thanks guys, Jeff

All other things remaining equal, the compression will go up, as you increase the bore. Larger swept area being compressed to roughly the same final volume (chamber).

Really? So if they say a piston will net a certain compression ratio at a specific bore and you were to bore larger and get the larger pistons the CR would actually go up from what was stated. See, this is why I have to ask questions like this. Completely opposite of what was happening when I tried to figure it out in my head, Thanks
Jeff

Here is a CR Calculator (http://members.uia.net/pkelley2/crc.htm) that you can play with. Try your dimensions and then change bore/stroke size and see what happens.

Thanks alot Pat, that is very helpful in understanding what effects compression ratio and how small changes in anything can make big changes in the compression ratio.
Thanks again, Jeff

Look at it this way. A 454 is roughly 7.4 litres, or 7400cc, so that means each cylinder of the 8 is roughly 925cc. So, that means you can fill 925cc worth of air in there(not including the combustion chamber). anyways, you asked about a 116.9cc chamber. Say your 454 has 925cc of air in the cylinder and the piston rises all the way up, compressing that air to the size of your combustion chamber of 116.9. So the air used to be a volume of 925cc, but now its all compressed in the combustion chamber, making it roughly 117cc. Now pretend you bore the motor over .060. That makes the engine displacement larger, and with the .060 bore, each cylinder is now roughly 953cc each(larger than 925). But, the combustion chamber size in the head does not change. That means you squish a larger volume of air into the same size combustion chamber. Sqeezing 953 cc of air into a 117cc chamber will make a higher compression ratio than sqeezing 925 cc of air into the smae 117cc volume. Does that help any? Keep in mind that all the numbers I used are just theoretical values. In real life, it wont work out so that your engine is always drawing in and compressing the exact amount of air that it can fit based on its displacement. Either way, the larger bore makes room for more air, yet once its all compressed into the combustion chamber, that doesnt change so you now have the potential for more air shoved in the same space, resulting in higher compression.

Remember though,the ratio is the difference between the TOTAL of the volume of the cylinder plus everything above it(the running clearance,gasket,chamber and minus dome volume if any or added if dished)then divided by the total of everything above the deck(running clearance,gasket,chamber,minus dome or added if dished ) :cool: