compression calculator

[MR.hp]

Thought this one is pretty good
http://kb-silvolite.com/calc.php?action=comp

I like the dynamic part

[Guest]

no workie....

[smooth_358]

it worked for me

[64fairlane]

seemed to work for me 11.1 to 1 dont know if its right but sounds good

[torkflight]

call me an idiot but in the dynamic part do I just add 15 to my intake closing number? so if my abdc # is 62 I want to enter 77? is this correct?

[64fairlane]

[jollywrencher]

call me an idiot but in the dynamic part do I just add 15 to my intake closing number? so if my abdc # is 62 I want to enter 77? is this correct?

yes I believe that's correct, they are trying to get seat to seat duration.

"Note that the calculator asks for the intake closing point at 0.050", plus an additional 15 degrees. I guess that's a somewhat decent substitute for knowing the "exact" valve closing point (which is, at best, an educated guess anyways - who's to say that the intake valve is leaking-down cylinder pressure at 0.009" of lift but not at, say, 0.007"?), but I'd rather use the "advertised" number. The 15 degrees that the calculator asks for is too small - adding in about 25 degrees would work for a relatively "steep" hydraulic roller cam like my Comp Cams Xtreme Energy (the difference in advertised and 0.050" duration being 52 degrees in this case), and something more like 30 degrees would be better for a traditional flat-tappet cam."

[big block fiero]

The only way to know the dynamic compression ratio of an engine is with in cylinder pressure/temperature measuring equipment or a multi-point indicator of which I use the latter to measure in cylinder pressure just before the plug fires. To prove this to your self just consider engine A vs engine B.

Engine A has heads that don't breath and engine B has heads that do yet this formula would have us believe that if the valve events are the same then the dynamic compression is the same between these two engines regardless of how starved for air the poor flowing engine is at higher rpms. Also notice that the dynamic compression is the same regardless of engine rpm. Some builders that I know just have a cranking compression pressure that they look for to achieve optimal torque for there fuel type.

I believe that this formula is just as useful as cranking compression numbers are but it would be misleading to call it dynamic compression ratio, maybe "effective cranking compression ratio" would be more accurate because your not out-flowing anything or testing Volumetric efficiency at that low speed.

[ramairws6]

Just use a whistler and you'll have the exact # everytime and it will be accurate! Used one on mine and I put it together expecting 11.6 and when we whistled it ended up being 11.3. After you get all the squish somethings bound to change! Traver

[torkflight]

Just use a whistler and you'll have the exact # everytime and it will be accurate! Used one on mine and I put it together expecting 11.6 and when we whistled it ended up being 11.3. After you get all the squish somethings bound to change! Traver

I dont know what you are talking about? Teach me

[ramairws6]

Whistler

A whistler is a gadget that Katech engineering out of Michigan designed that uses compressed air that you blow into the cylinder to find out what your exact compression is. It works awesome because it actually tells you what your exact compression is by filling all chambers with air, not what you think you should have by the parts you use and the mathmatical calculations you use to find it. When it fills up internally you turn it around and fill it all back into a test tube with measurements thats attached to the outside of the unit. I built my motor parts and calculation wise for 11.6 to one, but things change after it's all assembled.When I whistled it, it came out to be 11.3 only.Traver

[big block fiero]

But its still measuring static compression ratio. Were talking about something different, DYNAMIC compression ratio (while the parts are moving).


Still pretty neat though and a good informative post.

[ramairws6]

Well when I opened the calculator up it start out with 'STATIC' compression also and I seen somebody post there Static compression ratio on here a couple posts back so I figured thats what most were getting at?! Traver

[ramairws6]

Allright.................I looked back and seen what you mean. Oops? Traver

[torkflight]

A whistler is a gadget that Katech engineering out of Michigan designed that uses compressed air that you blow into the cylinder to find out what your exact compression is. It works awesome because it actually tells you what your exact compression is by filling all chambers with air, not what you think you should have by the parts you use and the mathmatical calculations you use to find it. When it fills up internally you turn it around and fill it all back into a test tube with measurements thats attached to the outside of the unit. I built my motor parts and calculation wise for 11.6 to one, but things change after it's all assembled.When I whistled it, it came out to be 11.3 only.Traver

where can I get this done??