quote:
Originally posted by Gazoz:
George could you please explaine the hydraulic roller cam intencity number.or if you already have in the past just direct me to were i should be?
It is the difference between the advertised duration and the duration at 0.050. It was conceived by Harvey Crane as an indication of a cam lobe's ramp rate. For most cam companies the advertised duration is measured at 0.006 tappet lift, it is supposed to be a standard that everyone adheres to. Hydraulic tappets are supposed to "lock" and start moving the valve after the plunger has been compressed 0.005 inch. So duration at 0.006 is a good indication of actual valve movement. But Crane (and others) has cams out there that are measured at 0.004 tappet lift. Measuring advertised duration at 0.004 tappet lift adds 8° to 10° to a cams advertised duration figure, it makes a cam look way bigger than it actually is.
In the 1970s hydraulic flat tappet cams had hydraulic intensities in the 65° to 70° range. Valve springs had 90 pounds seated force to prevent valve bounce. Today hydraulic flat tappet cams have 50° to 54° hydraulic intensity (some are faster yet) and valve springs have 115 to 130 pounds seated force. The cams in question, hydraulic roller cams, have 54° to 56° hydraulic intensity (occasionally I run across a lobe with 52°). I added 54° to the duration at 0.050 to arrive at my "estimated" duration at 0.006 figures.