Static and Dynamic Displacement and HP
It's not about cr just borrowed the words static and dynamic
And applied them to displacement, don't think most people can see past static displacement what the cylinders physically measure. Not what it displace over time, aka running engine, Cubic Feet per Minute, and how different static displacements can have same dynamic displacements and engines of similar power have similar dynamic displacement "cfm".
Oh yeah now I totally get you.
But, I think you can turn that around by thinking VE, it sorta comes to the same thing.
like if a 318 running at a particular rpm at 100%= a 360 running at 88%... but I think the physical dimensions of bore and stroke, will fudge the efficiency curves such that this can probably happen just over a particular rpm or at least, just a very small window of rpm.
I think the Wallace Calculator does a pretty good job of making this comparison, with their P/V(pressure to volume) index.
Wallace Racing: Dynamic Compression Ratio Calculator
V/P Index Calculation
stuffing the build specs of my engine into the Wallace I get this;
Static compression ratio of
11:1.
Effective stroke is
2.79 inches.
Your dynamic compression ratio is 8.79:1 .
Your dynamic cranking pressure is
184.87 PSI.
Your effective boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of PSI is 8.79 :1.
V/P (Volume to Pressure Index) is 159
now sticking a 440 Magnum in there, circa 1968, I get this
Static compression ratio of
10.5:1.
Effective stroke is
2.75 inches.
Your dynamic compression ratio is 7.97:1 .
Your dynamic cranking pressure is
162.75 PSI.
Your effective boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of PSI is 7.97 :1.
V/P (Volume to Pressure Index) is 157
Notice the nearly identical P/V numbers
They use this P/V number to compare the bottom end potentials of various engines, and indicate that engines with similar P/V indexs will have similar power... in what they define as; "the lower rpms" , and I assume to be, sub 3500
Here you can also see how the cylinder pressure contributes to performance in this zone; comparing my 367's CCP of 185psi to the 440 at 163psi.
Also notice that the effective strokes are very similar. My 367 is down to
286 effective cubes, compared to the 440 at
322 effective cubes, calculated from the effective strokes.
Now, I have never had nor driven a 440 Magnum, so I cannot say how powerful a bottom-end it has.
But you can come on over and take my car for a ride, and scare the crap out of yourself, lol, testing it's bottom-end.
They say there is no substitution for displacement, which, as for drag-racing which is all top-end power, that would probably be close to correct.
But on the street, IMO, there is no substitution for the P/V index
my previous cam ran this
Static compression ratio of
11.3:1.
Effective stroke is
2.86 inches.
Your dynamic compression ratio is 9.23:1 .
Your dynamic cranking pressure is
196.92 PSI.
Your effective boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of PSI is 9.23 :1.
V/P (Volume to Pressure Index) is 173
As you can imagine, with the stronger P/V of 173, I liked it a whole bunch more.
In this configuration, the effective displacement was
293 cubes
