7 replies to this topic

[Shtstr]

Hello everyone.
As the title says let's talk about the difference between static and dynamic compression ratio.

Most engines say around 9 to one static compression.
But the dynamic compression ratio is more likely between 7.5 to 8.5 to one.

So how does it change between static and dynamic compression.

Static compression is the entire cylinder with the full stroke and bore full of fuel and oxygen charge compressed into the top of the stroke and cylinder head chamber.

The dynamic compression ratio is also factors in the cam and rod length.

Here is a link to a on line calculator so you can work out what you're dynamic compression ratio is.
Please feel free to share your results.
I will kick off with my new engine I'm building atm.

http://www.wallacera.../dynamic-cr.php

[Shtstr]

Here's mine.

Attached Files

•  Screenshot_20210105-110857_Chrome.jpg   107.8K   5 downloads
•  Screenshot_20210105-110941_Chrome.jpg   171.94K   3 downloads

[Peter UC]

I was intrigued so here's mine.

 Dynamic compression.JPG   85.67K   7 downloads

 

[Shtstr]

I was intrigued so here's mine.
Dynamic compression.JPG

Quite a bit of difference hey.
Majority of people don't understand how this effects the engine and what fuel you can run.

Pump 98 can handle up to 9.7 to 1 dynamic compression ratio even though the static says otherwise.

[Lima31]

Just be aware that the Wallace race calc sheet gives a different V/P ratio than other textbooks, and the reference page it links to.

[Shtstr]

Just be aware that the Wallace race calc sheet gives a different V/P ratio than other textbooks, and the reference page it links to.

What one do you use?

[Lima31]

What one do you use?

Use the spreadsheet on the site linked on the page.

http://victorylibrar...ar/Formulas.xls

Edited by Lima31, 06 January 2021 - 02:08 PM.

[Shtstr]

Use the spreadsheet on the site linked on the page.http://victorylibrar...ar/Formulas.xls

Too much effort for me.
I'm just lazy and like online calculators haha