Quote:
Originally Posted by johnta1
What would the LSA be on them?
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Intake closing point determines start of compression or conversely amount of time in compression.
LSA and ICL are mere coincidences of chosen timing events. Best used for cam installation and inspection purposes.
To further follow Paul and Harolds statements. TRUE VALVE SEAT time is when full static compression starts. And here even a solid flat is usually far different than a hydraulic.
I recall Harold saying a solid flat can have as short if not shorter seat duration vs .050 than a roller.
Not so with a hydraulic as there is no clearance ramp.
.050 cam lift numbers are also best used for installation/inspection and secondly comparison purposes. Certainly shouldnt use .050" cam lift to guesstimate dynamic compression. Rocker ratio is part of reason why not. How fast and how many degrees sooner/later the intake shuts off is affected with rocker ratio.
Some of the biggest differences in cams from one brand to the other with seemingly similar/equal "specs" is in the numbers not advertised. That 1st .004"-.006" of lobe lift plays big roles in both valvetrain stability and staging of events. Sure not much is going to "flow" past a valve at .006-.009 lift but important pressure exchanges begin and end there.
One other point to consider.... as speed increases and ve improves... pumping losses decrease, plus any "boost" from exhaust "purge"/"scavenge" during overlap as well and you are going to trap more volume when the intake closes... Sooo...
In other words, dynamic cylinder pressures rise with VE and eventually VE (and torque/power fall off) drops and dynamic compression drops. Did you know compression also affects VE?
Dont crutch excess compression for the fuel being used...instead get the most out of the fuel being used by having the right compression and ignition timing for it. Yes cam timing does play a role but follow cam manufacturers compression suggestions. There is a reason!