I need help reading piston specs

[NukeBass]

The shop that restored my car told me the compression ratio in my 340 was around 9.75:1. I'm in the process of looking at getting a smaller camshaft for it so I'm looking at the relationship between cam timing and dynamic compression ratio and all of that fun stuff, so I figured I would try to replicate the 9.75:1 number as an exercise. All of the info I have is from the paperwork provided by the builder (nothing about CR written, though). From the paperwork, it has 68cc heads and felpro head gaskets, standard rod and stroke length and the pistons in the attached spec sheet. The pistons have a compression height of 1.84", which should put the pistons above the deck, but I'm having trouble figuring out what the valve relief specs on this sheet mean, and the CR seems to be fairly sensitive to those values. I also did an internet search for these and didn't find them in their catalog or on any websites. Does anybody have any insight? Thanks for your help.

 

[80fbody]

Go with +5cc if you have two valve notches on those pistons. That should be fairly close. You add cc's as the notches hold volume whereas a dome would take away from volume within the cylinder. Easy calculator below for static compression. There's also one on United Machine's site (KB pistons) that I use as well.

 

[NukeBass]

Cool, thanks!. It looks like I may be a bit closer to 10:1. The United Machine's calculator is pretty nice since it has static and dynamic in one spot.

 

[krazykuda]

Here is a thread that I wrote to find out your actual compression of your engine.
With it, you can find out what your engine actually is.

http://www.forabodiesonly.com/mopar/showthread.php?t=278215