Patrick, Tom,
JMHO, but I analyse a lot of valve train motion. Depending on what you want to do, you
might want to add more data to your testing regimen. Obviously, accuracy of measurement, has a
HUGE impact on the results, especially the derivatives.
Even if all you care about in your cam analysis is displacement, 10 degree interval increments at the crank is too "coarse" IMO. As Patrick stated, the measurement interval is so great that "unintended smoothing" of the data occurs, giving a false impression of the actual motion. And if you intend to make any assessment of derivatives, (velocity, acceleration and jerk), coarse data accumulation by hand will not give you anything but error filled data. To make "good" data driven decisions, well, the data has to be "good" to start with.
Things you can easily do, that will be helpful and give you better data:
1/ The best situation would be to have your cams "profiled" on a dedicated fixture such as a Cam Doctor, Cam Professional or Cam Analyst. This can be inconvenient and expensive, but gets you the best data available at the "non-manufacturer" level.
If you still want to accumulate data by hand, you can improve your accuracy by:A/ Decrease the measurement "interval". Every 5 crank degrees or better yet, 4 crank degrees is better than every 10 degrees.
2/ Increase the diameter of the degree wheel. This lengthens the arc segment per degree, thereby adding accuracy. A 16" diameter degree wheel is twice as accurate as an 8" wheel . . . . .
d/ Use an electronic indicator that reads in .0005" increments. .0002" or .0001" is better still. One with enough travel could be pricey.
These changes would give you "useable" data for velocity, probably for acceleration, probably not for jerk.
I no longer try to graph or analyse cam data in Excel. It is just too difficult to finesse the software to do what I want, as you both mentioned. I use cam specific software which is excellent and expensive, BUT, you can use a freeware program called DatPlot by Michael Vogt. It allows a second y axis, labeling freedom, and other controls that are tedious in Excel. Here is a link to some sample graphs.
https://vintageracing.online/threads/racing-engines-a-technical-examination.1092/post-11154Data entry in DatPlot can be more time consuming, there is no manual, etc. But, WTH, FREE!
Also, you want to take a hard look at things like lash ramps, transitional velocities, and seating velocity. These items can all vary based on the
ACTUAL lash.
Most cams have the same "rising ramp" because for a given tappet diameter there is a maximum velocity per degree that can be used before the cam runs off the edge of the tappet.
Sent you both a PM
Fordboy
