Calculating dynamic CR?
Calculating dynamic CR? So I'm looking at a certain cam grind and the specs on it call for an intake valve closing point of 43* ABDC. Using this recommended calculator http://www.kb-silvolite.com/calc.php?action=comp I get a static CR of 10.9 and a dynamic CR of 9.1.
That seems a little high for my liking, and higher than what the cam spec person said it would be (he mentioned this cam would get something like 8.6 dynamic CR).
Am I doing something wrong in the calculation? Is there a better calculator out there for this?
That seems a little high for my liking, and higher than what the cam spec person said it would be (he mentioned this cam would get something like 8.6 dynamic CR).
Am I doing something wrong in the calculation? Is there a better calculator out there for this?
Dynamic Compression Ration = Cylinder vol. + clearance vol. + piston Comp. vol. + gasket vol. + chamber vol. divided by Clearance vol. + piston vol. + gasket vol. + chamber vol.
Or just use this: http://www.wallaceracing.com/dynamic-cr.php
Or just use this: http://www.wallaceracing.com/dynamic-cr.php
It's a 222/226 eps lobed cam 114+2 (112 ICL).
The calculator above specifically calls for IVC @ 0.050 + 15.
Using the IVC @ 0.006 both of those give me 8.5 DCR so that makes more sense.
The calculator above specifically calls for IVC @ 0.050 + 15.
Using the IVC @ 0.006 both of those give me 8.5 DCR so that makes more sense.
Dynamic Compression Ration = Cylinder vol. + clearance vol. + piston Comp. vol. + gasket vol. + chamber vol. divided by Clearance vol. + piston vol. + gasket vol. + chamber vol.
Or just use this: http://www.wallaceracing.com/dynamic-cr.php
Or just use this: http://www.wallaceracing.com/dynamic-cr.php
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You're right. I have that written down wrong for some reason in my spreadsheet.
That first Cylinder Vol is measured differently. It's done this way:
Cylinder volume for Dynamic Compression ratio = 0.7853982 x bore2 x DST
DST = ST - ((PR2 + 1/2ST) - RL)
ST = stroke
RL = Rod Length
PR2 = Piston Rise from crank CL (PR1 = sq root of ((RL*RL) - (RD*RD)) - (RR = 1/2ST * (cosine ICA))
RR = Rod Distance in inches below crank CL; RD = 1/2ST * (sine ICA)
RD = Rod horizontal Displacement in inches; RR = 1/2ST * (cosine ICA)
Or something.
That first Cylinder Vol is measured differently. It's done this way:
Cylinder volume for Dynamic Compression ratio = 0.7853982 x bore2 x DST
DST = ST - ((PR2 + 1/2ST) - RL)
ST = stroke
RL = Rod Length
PR2 = Piston Rise from crank CL (PR1 = sq root of ((RL*RL) - (RD*RD)) - (RR = 1/2ST * (cosine ICA))
RR = Rod Distance in inches below crank CL; RD = 1/2ST * (sine ICA)
RD = Rod horizontal Displacement in inches; RR = 1/2ST * (cosine ICA)
Or something.
Last edited by JakeFusion; Jun 1, 2013 at 01:00 AM.
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