Compression Ratio (static / dynamic) and more calculator

914fan · Post by **914fan** » Mon Mar 28, 2005 12:05 pm

I have compiled and built a excel sheet that calculates your compression and other values. I would like to post it here for everybody to use. I feel that is would be a good tool for building and dreaming up your next engine. I cannot guarantee its accuracy but can say that it is within the range of answers most on-line calculators provide. This would be a good guideline but I will recommend doing the math yourself or double-checking with other calculators.
**I accept no responsibility for any damage caused by using this sheet.**

Having said that can someone tell me how to post it?

tuna · Post by **tuna** » Mon Mar 28, 2005 12:10 pm

Send it to me via email and I will host it on my website.

Tuna

914fan · Post by **914fan** » Mon Mar 28, 2005 12:27 pm

Tuna,
You have mail.

tuna · Post by **tuna** » Mon Mar 28, 2005 8:01 pm

Here's the calculator. It looks pretty good and I'm sure I'm going to lose many hours of my life playing with it.

Tuna

914fan · Post by **914fan** » Mon Mar 28, 2005 9:04 pm

Thank you for hosting it Tuna.
I hope it helps someone. I feel sorry for all the computers that now have to burn thier processors on it. Mine has been running it almost constantly.

Lets see if I change this then I get OOOOOHHHHHHH

and this AAAAHHHHHHHH

Lots of fun.

Enjoy all

dstar · Post by **dstar** » Tue Mar 29, 2005 12:51 pm

Where do we input overlap, duration, lobe centers, things like that.

Don't they contribute to *dynamic* CR?

Don

914fan. · Post by **914fan.** » Tue Mar 29, 2005 3:27 pm

Dstar
On the calculators I looked at the only cam info they wanted was intake closed at X. I do not know if there are more variables involved. If there are and someone can tell me how they are involved and I will try to incorporate them.
I was under the impression that dynamic compression was basically the same as static except that your stroke was what ever was left when the intake closed.
I could be wrong.
Let me know what you think. I would like to provide the best sheet I can. It helps me as well as you to have correct data.
Feel free to modify the sheet to suit your needs.
Thanks

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Tue Mar 29, 2005 4:29 pm

914 fan, want to make some sheets for me? I need some of mine revised.

Guest · Post by **Guest** » Tue Mar 29, 2005 8:08 pm

Jake,
If there is something I can do for just let me know. God knows you have helped me plenty.....

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Tue Mar 29, 2005 8:09 pm

Cool. I'll email you!

914fan · Post by **914fan** » Tue Mar 29, 2005 8:11 pm

Hey you beet me to it....

And I even forgot to log in.....

914fan · Post by **914fan** » Tue Sep 06, 2005 6:46 am

Tuna
This is the calculator I was reffering to.

HAM Inc · Post by **HAM Inc** » Tue Sep 06, 2005 9:57 am

This will come in handy! Thanks for the effort.
As for dynamic compression that's another matter. The intake valve actually closes as the piston is on the way up the cylinder on the compression stroke. Determining dynamic compression is trickier than just calculating the cylinder volume when the intake closes and using that measure for swept volume. Overlap won't figure into this calculation.

Dynamic compression is also going to encompass the volume of air that ACTUALLY flows into the cylinder. (Overlap can effect this) This will vary with RPM's. It would take a very sophisticated program to accurately calculate dynamic compression, and the input data would have to include intake flow data, rod/stroke ratio, and a host of other info. plus the many intangibles that come into play when the engine is running that effect cylinder filling.
The truth is actuall dynamic #'s would be meaningless (at least to me) until performance trends were estasblished relating to different values. Two engines with identical displacement and chamber volumes will have radically different dynamic ratios if the heads flow #'s are different and/or intake valve closing specs are different.
FYI the intake valve closing event is the most important of the valve events.

dstar · Post by **dstar** » Wed Sep 07, 2005 9:43 am

HAM Inc wrote:FYI the intake valve closing event is the most important of the valve events.

Yes, I am aware of that, but wouldn't an engine be more
*efficient*, i.e. make more power, if the intake valve closed right
@ BDC of the intake phase, instead of a few degrees after??

I'm trying to figure out the best *clock* to install my Annihilator
cam that I bought from Jake.

Don

speedy57tub · Post by **speedy57tub** » Wed Sep 07, 2005 10:02 am

Nice spreadsheet! It looks a lot like mine but I used MathCad for mine. Thanks for this one, due to the software, it should work with most PC's (unlike mine).