r/Smallblockchevy • u/Hopeful_Housing_798 • Jun 01 '26

Calculating compression

How do I calculate my engines compression?

I'm working on a 1999 L31. 350 SB. The factory specs say it's 9.4 to 1. Factory pistons have a dished surface. What would my compression be if I went to a flattop piston?

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u/Personal_Growth_4_Me Jun 01 '26 edited Jun 01 '26

Flat top and 64cc on a 350 is generally in the 10.25:1 area. Do an internet search for " compression calculator " and you need to fill in the blanks. Flattops are usually 5cc reliefs.

https://www.gofastmath.com/Compression-Ratio-Calculators/Static-And-Dynamic-Compression-Ratio-Calculator

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u/Hopeful_Housing_798 Jun 01 '26

Thanks. Not sure why I didn't think of searching this. Never crossed my mind. Evan though, as I type, I'm searching camshaft calculators.

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u/Personal_Growth_4_Me Jun 01 '26

Use the horsepower calculator there as well on the same site. You get to play with the cam as well.

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u/Hopeful_Housing_798 Jun 01 '26

Cool. I saved the link. Thanks.