again.........terminology......... what he describes in that link isvolumetric pressure..........akavolumetric efficiency and its effect on pressure............very different thananything you describe as either dynamic compression ratio or static compression ratio.

boyles law....... reduse volume by half and pressure is doubled, do the math with this from your intake closing ABDC to TDC and your pressure will be MUCH less than you would actually measure on a cranking engine at any speed piston movement from BDC to TDC

Also, the CORRECT formula for cylinder volume is (Pix(radius ofboresquared))x (Stroke)

the .7854 is a lamans formula thats faults are more dramatic at higher bores. try both formulas at different displacements and you will see what i mean.the answers will be close at small bores.......... but will differ to a large enough degree within the displacements of large v twins. (the correct mathmatical formula is basically the formula to find the area of a circle(which cannot be done accurately without Pi) multiplied by stroke)

I don't know who that guy is, he has some interesting ideas.........but is a bit off when it comes to true engine math, and even says that most of the math is too complex for him (even though that whole paper is about math!!)

this may not be your first rodeo, but that doesn't mean you can stay on the bull for 8 sec.

 

I can see that this is going to be a case of everyone splitting hairs. I am very familiar with your 'correct' formula for cylinder volume. But, if I'm standing at a workbench explaining this to someone who doesn't have a clue, I point to the formula that I quoted, that I have penciled on the wall. Most people prefer layman's terms to absolute precision. I use precision for my own purpose. I demonstrate in layman's terms. Pi is inmy equationfor calculating cylinder volume. 0.7854 is in most common text, along with the formula. That's why I chose it.

And, I'm not trying to compare myself with Mr. Diamond. I still admire him for the time he has taken to write what he has. Any issues with his math must be taken up with him. I did not provide his link, to make comparisons with volumetric pressure/efficiency. I provided the link, because it displayed some very common formulas, including the one(s) for'compression ratio'. Which is still the only thing I've been discussing here. None of the rest. What is it about discussing a ratio that's so hard? My whole point (and not what anyone else claims that I'm trying to say) is that I'm discussing what happens when the intake valve closes ABDC, the piston moves up to TDC, and the comparison of the ratio from no compression to full compression. Where in this simple statement do you get an error in terminology?

And, if you still want to say that I'm talking about something else, just let it go. I'm sorry that this fellow's thread was hijacked by this discussion. I'm sure that he's plumb sorry that any of this was said.

As to the bull, there ain't been one that whipped me yet. I'm not in it for the time. I'm in it for the fun. And the ride!

Jack

 

Thanks Jack You cleared up a few points for me.

 

My pleasure.

Jack