BIG cam question........only 125psi cylinder pressure
03-06-2005, 09:01 PM
#21
Launching!
Patrick G is correct. As I not very clearly tried to explain in my post, if you use the .050 numbers you will not get a correct result for cranking compression. I used my assumed figure of about 300 degrees advertised duration for your cam to come up with the 80 degrees ADBC figure I plugged into the calculator. You might have the actual advertised duration.
Another side note on this calculator page - it also incorrectly furthers the fiction that more overlap will lead to less dynamic compression. Overlap occurs on intake valve opening, while dynamic compression is controlled by the intake valve closing point. Increasing cam duration obviously leads to a later intake close, but so does a higher intake center line spec. So if you take two cams of indentical duration, but grind one with 106 ICL and 110 lobe separation, the other with 110 ICL and 114 lobe separation, the second cam will have less overlap but also less dynamic compression.
Another side note on this calculator page - it also incorrectly furthers the fiction that more overlap will lead to less dynamic compression. Overlap occurs on intake valve opening, while dynamic compression is controlled by the intake valve closing point. Increasing cam duration obviously leads to a later intake close, but so does a higher intake center line spec. So if you take two cams of indentical duration, but grind one with 106 ICL and 110 lobe separation, the other with 110 ICL and 114 lobe separation, the second cam will have less overlap but also less dynamic compression.
