what's my new compression ratio
03-14-2013, 01:38 PM
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what's my new compression ratio I had a stock lm7 5.3l that was 9:1 I believe from factory , the heads where milled down to 58cc chambers from 61.5 , what is my new comp ratio
03-14-2013, 02:38 PM
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The LM7 5.3L truck engines are 9.45/1 and to find out You're compression go to Wallace Racing and go to there engine calculators ,,,,,,,they have at least 150 different calculators for engines and 1/4 and 1/8th mile times gear ratio changes ,,,,,,,,,,etc . You'll be plugging 3.779" bore 3.622" stroke deck height of say .015" combustion chamber size in cc and piston dome or dish ,,,,,,the LM7 has 9cc of dish so that's +9cc,,,,,,,if the pistons were domed you'd plug in minus whatever the # was and the .015 is minus also because the pistons at TDC come out of the hole
03-15-2013, 12:22 AM
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either the calculator doesnt work or the numbers im using are wrong, because plugging in the stock figures for the lm7 doesn't yield anywhere near 9.5 it comes out at like 10 and change
03-15-2013, 11:26 AM
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The calculator I always use requires a negative number for a dish piston. I come in right at 9.5 CR using 8cc piston dish. I also used 61cc for the heads, technically the 5.3 heads are 61.15cc. Deck height is usually about .006-.008 out of the hole. I just used .007 for this estimate. If everything else is left the same, changing the heads to 58cc gives you "about" 9.83 CR.
http://www.csgnetwork.com/compcalc.html
http://www.csgnetwork.com/compcalc.html
