Dynamic & Static Compression Ratio Calculator

[Indycars]

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

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 calculation at a time when online, not so with this Excel spreadsheet...you
can see all 5 versions at the same time !!!

Please page down to my latest post, and use that link to DOWNLOAD the latest version of the Excel spreadsheet file.

 

[tmhutch]

Does this download still work?

 

[Indycars]

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.

 

[tmhutch]

OK, got it. Thank you.

 

[Mike]

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

 

[Indycars]

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.

 

[Indycars]

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.


Altitude above Sea Level and Air Pressure



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:

 

[DavidLee]

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'.

 

[Indycars]

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.

 

[Indycars]

I wanted update my Static/Dynamic Compression Ratio calculator (SCR/DCR) Microsoft Excel calculator download.

I've had very little feedback about the Cranking Compression on real world engines, but with the two engines that I have it's been very different. So you will need to take the Cranking Compression calculation with a grain of salt as they say. Version 4 (latest until the DL below) has a adiabatic constant of "1.2", but with the 2nd engine feedback I raised this constant to "1.24". This raised the cranking compression from 178 psi to 195 psi while using the same parameters. See Engine #1


.