ok im real confused about when crower or crane cams posts "advertised duration" and "duration @ .050" Can some explain this??

 

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OK, I'll try. Duration is the amount of degrees the valve is held open by the cam. It is actually hard to tell at exactly what degree # the cam starts to open. This is because of something called a clearance ramp which is ground in the cam to slowly lift the valve for the first few degrees.
In order to compare the usefull amount of duration in two different cams, duration is listed as beginning and ending at a certain lift. Some start the duration at .010" or 1mm or .020" or .040" or .050".
An example of measuring a cam might be..total duration at 0 lift of 280 degrees, .010 lift at 265 degrees and .050 lift have 250 degrees of duration.

Two cams could have 280 degrees of duration at 0 lift but one could have 250 degrees duration at .050 and the other only have 235 degrees at .050. The 250 lift would be the wilder of the two cams.

You can only compare duration between two different cam manufacturers by knowing at what lift the duration is measurered

 

This is when a degree wheel comes into play. With it and a dial indicator, you measure it yourself. You can also find true tdc for the block and head. Then use your cam gear to dial in the cam.

I think one is good stuff.

 

In GENERAL , what have you guys found to be the difference in degrees when a cam is measured at .050" and 1mm. (Obviously it'll have more duration at 1mm than .050').

 

1mm=.040, so degree diff between .040 and .050, depending on the rate of lift of the cam, would be between 5-10 degrees as an estimate.