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Does compression alone create horsepower?

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  • Does compression alone create horsepower?

    Here's something I don't think I ever figured out. If you have two engines, identical in every way except for the compression ratio, would the one with a higher compression ratio make more power?

    As an example, say you have two old school 350 Chevrolets, one with 9.5:1 and one with 10.5:1. All other components of the engines are idenical. Does the one with 10.5:1 make more power?

    www.TrackHQ.com

  • #2
    I'd say yes, more power. The reason being you get to ride more of the bang and waste less of it.

    Suppose you had almost no compression ratio. You'd make a lot of fire but wouldn't do much.

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    • #3
      Blah blah octane, blah blah timing...

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      • #4
        Thinking about it more, would there be a geometric increase as compression ratio rises? Taken further, for example, let's say you had four identical 350 Chevrolets. 7.5:1, 8.5:1, 9.5:1 and 10.5:1.


        The power gains are greater as compression rises. In other words, expressed as a percentage, the power gain from 9.5 to 10.5 would be greater than those from 8.5 to 9.5 and from 7.5 to 8.5.
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        • #5
          Logarithmic, aka diminishing returns I think.

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          • #6
            I'm betting on a parabolic curve, normal distribution.
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            • #7
              This topic is click bait for engineers.
              Look it up yourself
              Start with Carnot
              Pronounced car know

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              • #8
                A good overview:
                https://dsportmag.com/the-tech/boost...sion-benefits/

                . . . .Or see the "bottom line" formula below.

                Click image for larger version  Name:	Capture2.JPG Views:	0 Size:	31.5 KB ID:	263804

                The "full Monty" - a very comprehensive article, including discussion of octane, and boost vis a vis compression:

                https://dsportmag.com/the-tech/educa...tio-101-part2/
                Last edited by Loose Caboose; 02-25-2020, 04:12 PM.

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                • #9
                  Looks like the returns are indeed decreasing. Maybe not log-decreasing...

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                  • #10
                    In relation to your Miata build, I would suggest that your aspiration is to be as close as possible to 9.50000000 as possible.

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                    • #11
                      Originally posted by CoolTech View Post
                      In relation to your Miata build, I would suggest that your aspiration is to be as close as possible to 9.50000000 as possible.
                      Agreed.

                      www.TrackHQ.com

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                      • #12
                        Originally posted by robburgoon View Post
                        Looks like the returns are indeed decreasing. Maybe not log-decreasing...
                        Natch!

                        I'm not a science/math/engineering guy; but -plugging in numbers - it is increasing because the fraction inside the parenthesis is a larger numerator when the compression is increased; and no exponents hint at a non-log function.

                        Plus, why would anyone increase compression anyway if it reduces output?

                        Or not . . .

                        I

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                        • #13
                          Returns decreasing. Still going up, but less and less quickly. As in, going to 2:1 to 3:1 is awesome, 11:1 to 12:1 not nearly as awesome. Aka diminishing returns. But yeah, probably no logs or exp here.

                          Edit: Would be amusing if there was a stealth exponent from calculation of volume for calculation of ratio... but probably not, hehe. I have better problems to think about.
                          Last edited by robburgoon; 03-02-2020, 05:40 PM.

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                          • #14
                            Thanks.

                            I misunderstood (all too typically) your word "returns" to mean "results". Hence, my very boneheaded question. :-(

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