octanejunkie
Mopar Padawan
You need tools for checking the chamber cc's. I don't know if you do E-bay but if you do here is a cheap kit that'll do it. Just make sure and clean the chamber and valves good so you get an accurate reading.
http://cgi.ebay.com/ebaymotors/ws/e...0395360749&viewitem=&sspagename=STRK:MEWAX:IT
Then you check to see how far down the hole the pistons are. There are a few ways of doing it but I find TDC with a dial indicator then lay a straight edge across the deck surface and stack feeler gauge blades until you reach the piston then add them up and that's how far down the hole the piston is. If the pistons have valve reliefs that'll add cc's to the equation. They vary so it's best to look up the pistons and see what it's rated at since you can't really get in and cc them easily with the lower end together. Then you go to the website octanejunkie provided and plug in all the numbers and it'll give you your compression.
FWIW I put my own CC kit together, I have a thread on it here with pics, it cost me all of $8 plus some grease and bottled water, of course you can use any liquid you want... just remember to be as consistent as possible with filling in the syringe and put the hole in the plexi plate at one "corner" of the chamber - I pitched the head in such a way that the air was forced to the corner where the hole was - easy peasy
Once you have all your chamber measurements (I did each chamber twice) you need the rest of the measurement as fishy described. For deck height I prefer a dial indicator on a magnetic base zeroed on the deck surface but the feeler gauge method works fine, I just don't like relying on having to compress multiple leaves of a gauge against a straight edge, too much margin for error IMO, unless you bolt the straight edge to the block. If you have a metal supply house near you get a rem piece of 1"x1" cold roll bar stock about 2' long and lay it across the length of the deck, use a few bolts and clamp it to the deck in the head bolt holes - if you are really industrious you can drill the bar and bolt through it - BTW this won't work too well if your pistons pop out of the bores, check that first ;) you want to measure the flat of the piston or the tallest point if it is a domed piston.
Once you have the deck heights of all 8 pistons, you can average them if they are super close (within .005 of each other) or use the smallest measurement you got as it will give you the highest compression value, then plug into the CR calc and off you go - erring on the side of caution is always better that is why you use the tallest piston rather than the deepest or a median measurement
As far as piston volume, look that up as fishy recommended, almost impossible to measure accurately at home. Then select a gasket like the fel-pro Z1008 (4.180" bore by .039" compressed thickness) or the Mopar P4120093 (4.060" x .040" compressed thickness) and you are pretty much there.