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Old 09-17-2003, 09:25 AM
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piston dome cc

I'm trying to figure out the compression ratio on this chevy big block, I'm not sure how to find the piston dome cc's, they are supposed to be .030 over 402's with 350 dome? I have a part #, but not at this moment, do I make a casting out of clay and fill it that way?

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Old 09-17-2003, 10:45 AM
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The piston manufacturer should have the compression ratios listed in their specs. It depends on the combustion chamber size of the head, head gasket thickness and the deck height of the block. Usually, the manufactures specs are close, all things considered, but after head milling and block decking, its not going to be too accurate.

Probably the more important thing to check is the "quench" distance. Its the distance between the outer flat edge of the piston from the gasket surface of the head. Engines seem to work best with that distance set at .044". That distance includes the head gasket thickness too. Most machine shops should be able to check this and make the necessary block deck milling operations to achieve that distance.
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Old 09-17-2003, 11:32 AM
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I'm trying to put the specs in my dyno2000, but I need the piston dome cc's, I have all the other specs, and the machine work is done, I just want to figure it for sure, or as close as possible? It has.0-.005 deck height, with the .035 gasket should put my quench at 35 to 40. The heads were 112, but they have been shaved, so I'll cc them again!
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Old 09-17-2003, 04:50 PM
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If you have the stuff to measure CCs its real easy.
With rod attached to crank get piston positioned in cylinder so that piston dome it even with deck. Now use a depth micrometer or dial caliper to measure how far down piston is in hole.

Calculate the volume of cylinder using your measurement, write that down.
Then use some grease to seal edges of piston, place your plate with little hole it over cylinder (use grease there too, duh) and use burret to measure the area around dome.

Subtract your measured volume from the calculated cylinder volume and you have the dome size.

When youre all done be sure to soak up all the liquid. I use water I know some people recommend different but it only climbs on edges of burret about .2 cc which isnt enough to worry about.
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Old 09-18-2003, 07:39 AM
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Thanks Greg, I'll have to get my calculator out, but that beats the clay idea!
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