CamKing wrote: ↑Sat Feb 08, 2020 2:29 pm
There's nothing Dynamic about DCR, and it has no mathematical significance to what's going on in a running engine.
DCR is based on the misconception that you need the intake valve to be closed, to start compressing the mass in the cylinder, and that's far from the truth. As long as the pressure above the intake valve is higher then the pressure below the intake valve, the open valve will not bleed off any compression.
Mike you're exactly correct ... nothing "dynamic" in the Internet's DCR definition
the Internet's popular inaccurate DCR definition : Dynamic Compression Ratio
there is nothing "Dynamic" in the DCR or Dynamic Compression Ratio ... as defined by popular Internet DCR calculators .
Definition of Dynamic : "marked by usually continuous and productive activity or change"
there's NOTHING changing in the DCR calculation .... its just as STATIC a calculation as the Static Compression Ratio !
the Internet's DCR should really have been termed or named something like IVC Compression Ratio ... instead of Dynamic Compression Ratio
BEFORE the Internet existed ... Dynamic Compression Ratio as SAE ( Society of Automotive Engineers ) defined it as also including effect of "Trapped" Volumetric Efficiency
and no degreed Engineer
before the Internet , would use the term "Dynamic Compression Ratio" without referring to "Trapped" Volumetric Efficiency
Trapped VE% changes with things like RPM and Throttle CFM, and affects the real "dynamic" DCR of an engine.
Trapped VE% was always part of Dynamic Compression Ratio definitions "before" there was an InterNet !
Basically,
InterNet DCR version is analogous to Static Balancing your Car Tires
SAE ( Society of Automotive Engineers ) 's DCR version is analogous to Dynamically Spin Balancing Engine Rotating Assembly ,
that is , imbalance or balance will
"change" with changes in RPM ( Cylinder pressure will change with changes in RPM )
a little history on the Internet's popular DCR calculation and inaccurate definition :
many years ago , Pat Kelley along with a VB6.0 Programmer , created the DCR Calculator
Pat chose 0.006 or Seat-to-Seat Durations , and his Calculator became widely accepted as true DCR defintion, but it was actually a wrong definition !
http://cochise.uia.net/pkelley2/DynamicCR.html
way back then, around same time as beginning of Pat's DCR , a very popular real lead-Engineer at Edelbrock , Jim McFarland started his own Website/Forum,
which i visited and saw a few Internet Kiddies/Newbies harrasing and telling Jim McFarland how wrong his defintion of Dynamic Compression Ratio was
and how Pat Kelley's DCR defintion was correct one
however, if you went to Pat Kelley's DCR website , even Pat Kelley stated this
a Quote from Pat Kelly : Two important points to remember:
The DCR is always lower than the SCR
The DCR does not change at any time during the operation of the engine
as Pat Kelley knew or realized that his DCR definition does not really CHANGE ... that its actually STATIC
Pat still named his Calculator a DCR Calculator ... which is a wrong definition !
and sadly his DCR definition became super popular across the Internet
and replaced the real Dynamic Compression Ratio defintions SAE Engineers had used way before the Internet existed !
Many years ago , corresponding by Emails with Pat Kelly , he admitted to me that he was wrong in naming his calculator "DCR" ,
but at that time could not come up with a better name
Pat also asked me if it was OK to place my Spark Plug Reading Pictures in an article on his website here :
http://members.uia.net/pkelley2/sparkplugreading.html