how to find compression

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hw612

hw612

The Mopar Martian.
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on summit's website i was looking at 440 pistons(kb hypers) and it dose not say the compression ratio, is there a way i can find this? .030 over bore, stock 906 heads 79cc i believe.
 
there's a ton more to it than that. On the KB web site at the top, it says tech info. click on that and then on calculators. you'll see the compression calculator. enter all that info and you'll get a very accurate estimate.
 
Their calculator is pretty good, but you can always send them an email too. I sent a few messages back and forth with a tech at KB to get a better estimate for my 340, since the tops of the pistons (KB243's) were actually over the deck of my 340. Since part of the piston was over the deck, but the valve reliefs weren't entirely, and the shoulder of the piston was pretty much 0 deck, it got a little bit more complicated then the generic info on the piston. But they were very helpful, and I got it figured out. :-D
 
The compression numbers piston manufactures advertise assumes the block deck height is at its nominal dimension, on an untouched block they are almost always significantly higher. Same with the chamber size they are almost always bigger than the nominal advertised number. If you just build an engine without measuring deck height or cc'ing the chambers you can be pretty confident that what ever the advertised compression ratio of the pistons are the engine will be 1 point or more lower.
 
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