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Dynamic & Static Compression Ratio Calculator

Discussion in 'T-Bucket Engine and Driveline Articles' started by Indycars, May 5, 2011.

  1. Indycars

    Indycars
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    This Excel file will calculate Dynamic and Static Compression Ratios for 5 different engines and show you the results side-by-side. If you don't have the "Intake Valve Closing Angle", there is also a calculator for that on page 2.

    I prefer this to online calculators. I can save my results and review them later, can't do that with the online versions. You can only look at one calculations at a time when online, not so with this Excel spreadsheet...you can have 5 versions all at the same time !!!

    You will need Microsoft Excel 2007 or you can download "Open Office" for FREE herehttp://www.openoffice.org/. Open Office can open and work with Excel spreadsheets. If you have an earlier version of Excel, then you can install the “Microsoft Office Compatibility Pack”, it’s also FREE from Microsoft.

    Comments and suggestions are welcome!

    Use this link for information on how to install the Office Compatibility Pack:
    http://support.microsoft.com/kb/923505

    Download Excel Calculator Here:
    DynamicCompressionRatioCalculator.xlsx


    Below is what the first three page look like.

    [​IMG]

    Second Page (Intake Valve Closing Angle Calculator) View attachment: IVCAngleCalc-2.jpg
    Third Page (Intermediate Results) View attachment: IntermediateCalc-3.jpg
     

    Attached Files:

  2. tmhutch

    tmhutch
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    Does this download still work?
     
  3. Indycars

    Indycars
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    You will have to be logged in for the links to work. But you are right only the bottom link works, out of the two possibilities.


    [​IMG]
     
  4. tmhutch

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    OK, got it. Thank you.
     
  5. Mike

    Mike
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    I've repaired the text link, so both will now work.
     
  6. Indycars

    Indycars
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    Mike,

    Is there a way to tell how many times a file has been downloaded??? I was thinking about adding a theoretical cranking pressure to the Excel calculator, but if its not being downloaded then it may not be worth the trouble.
     
  7. Indycars

    Indycars
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    The spreadsheet for calculating compression ratios was a great fit for adding the
    cranking pressure to. The DCR and SCR will not change with a change in altitude,
    but the cylinder pressure will most certainly change. So if you live at higher altitude,
    then you might want to consider comparing your DCR/SCR to others at sea level.

    Let's look at the example below. With a 2000 foot change to a higher altitude,
    you have to adjust the atmospheric pressure by 1 psi. (See the table below from
    the Engineering Toolbox website.) That means you could decrease the combustion
    chamber volume by 4.7 CCs to return to the same cranking pressure.

    So at 2000 feet, a DCR/SCR of 10.65/8.34 is equivalent to 10.07/7.91 at sea level.
    CrankingPressureExample01.JPG

    Altitude above Sea Level and Air Pressure

    AtmosphericPressureVsAltitude.JPG

    I also corrected an error in one of the calculations. So if you have the older one
    above, then download this one for the latest version.

    The calculator predicts 171 psi for my engine, but when I did a compression test
    the actual pressure was 185-195 psi. Only the last cylinder tested showed 185 psi,
    all the others were 190-195 psi.

    Could also compare the theoretical 171 psi to the Average actual compression
    of 192.5

    Download the new file below:
     

    Attached Files:

    Spanky likes this.
  8. DavidLee

    DavidLee
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    SCR and DCR are good tools, to help you predict your cranking compression, or CrCo for short, but in the end, CrCo is the best tool of all. On pump gas, 180-200 is the ideal. Anything under 140 needs help. Anything over 215 needs better than 93 octane.
    Air density drops by roughly 5% per 1500' elevation, so use goo gle to find your elevation, then your observed CrCo divided by your density correction gives you your CrCo at sea level. So if you crank 200 at sea level, you'll crank 170 at 4500'.
     
  9. Indycars

    Indycars
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    I'm closing my Dropbox account so many of the link will stop working for all my posts that have a download [most likely an Excel or PDF file, not photos, they are uploaded to the forum], not just this one. But if I could edit my posts, then I could correct the links so they continue to work.
     






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