LET'S TALK ABOUT DYNAMIC COMPRESSION, SHALL WE?

I don't know the specifics, but after reading some stuff on fuel octane vs. static & dynamic CRs by a guy named Tim Wusz (I think) who used to work for Union 76 and moved to Rockett, it was obvious that it's a real balancing act to try to push the static CR too high w/ octane-limited fuel. Even the "big camshaft" band-aid approach only works up to a certain point in the RPM range (the example Tim W. gave in what I was reading was 7000), beyond which the engine was still probably going to encounter issues from insufficient octane.

Because I deal with street engines I use the DCR fairly often. I think if you have a certain fuel type (meaning octane) to run, not taking into account DCR means you're overlooking a crutial ingredient. It's a much better way for me to predict the low speed potential for detonation. I also agree that as rpm rises it's importance is reduced. If you can run any fuel type you want, I dont think it's as critical because you can always use the fuel to stay away from the problems too much pressure for a given chamber brings.

The Dynamic Compression ratio is a calculated value.
Here is some interesting cylinder computations to compare:
Example is a theoretical stock 440 HP engine with 10:1 static compression.
The piston swept volume is 54.97 (x8 = 439.72cid.)
The total chamber volume includes all the chamber area above the piston at tdc. for out 10.09:1 compression ratio the Total chamber volume is 61.01 (x8 = 488.11cid.)
if we use stock cam specs, the intake would close at 67 degrees after bottom dead center.
The piston position or effective "stroke" calculated from the closing point is 2.726"
=(stroke/2)+rodLength+((stroke/2)*(COS(IntakeClosinPoint*PI()/180))-SQRT((RodLength^2)-((stroke/2)*(SIN(IntakeClosingPoint*PI()/180)^2))))

The new Effective swept cylinder volume = 39.96 cid (calculated the same as swept cylinder volume.) Interesting the total engine swept displacement now is only 319.65 cid,
and total engine volume (with heads space) = 368.04 cid.

What is interesting, it that the new displacement very closely responds to the low speed Volumetric Efficency (VE.) = 73%

The new Dynamic Compression ratio = 7.61:1

Assuming sea level air pressure of 14.7 psi, the estimated cylinder cranking pressure is 153psi assuming this calculation is correct:
=(DynamicCompressionratio^1.2)*AirPressure-(AirPressure)
Above you have to subtract the one AirPressure to get the gauge reading, otherwise the calculation would be the absolute cylinder pressure in the chamber.
The formula I have for low end torque is = 322 (AbsoluteCylinderPressure*EffectiveCylinderSweptVolume*NumberOfCylinders*0.006)

As air speed increases at higher RPMs, the inertia in the ports will overcome the pressure caused by the upward moving piston (also there is less time for this to effect the incoming charge), so more and more air is trapped in the cylinder increasing the VE of the engine. I guess you could call this Dynamic Compression, but it involves knowing intake and head port flows and velocity. Because VE is calculated on swept volume and not total chamber volume it is possable to have over 100% VE in a normally asperated engine.

I have to give credit to Panic Tech Papers @ http://victorylibrary/mopar/cam-tech-c.htm
for all the good info and formulas noted above.