Having spent time on the dyno in Georgia, PA, Virginia, and NJ. I have always wanted to know why they differ so widely. Below are some of the answers. Some of you have had similar experiences.
The Story Behind the Dynojet Chassis Dyno. This is a excellent read if you have the time.
http://hotrod.automotive.com/23395/1...yno/index.html
Beat the Drum
The crooked dyno operator can reprogram the weight of the drum, which will allow the dyno to create anomalous power numbers.
The High Ground
The same crooked dyno operator could elect to change the elevation value in the computer, which would have a critical impact in power generation. Naturally aspirated engines are especially susceptible to this ploy.
Change Load
Changing the load by tightening or loosening the tie-down between runs can compromise any comparisons made with the dyno testing.
Different Day Dynoing
This one can be hard to avoid if you are having extensive work done. Check to see if the dyno in question has a weather station that can correct for any big differences. Beyond that try to arrange testing for about the same time of day as baseline runs were performed. This will lessen the effect.
Correction Factor
A key element to producing comparable dyno charts on a global basis is the Correction Factor, SAE Standard J1349, which applies the following weather station data--atmospheric pressure 29.23, air temperature 77 degrees Fahrenheit and humidity 0 percent--to all tests. These exact figures allow apples-to-apples comparison of runs from different cars, different facilities, etc. So graphs with SAE-corrected power were made to this standard. The dyno in question must have a weather station and the proper software in order to generate SAE-corrected data.
Smoothing
An option on Dynojets, smoothing takes a jagged graph and delivers a more readable curve. Smoothing of the graph can be done by entering a value between one and four at the appropriate place in the computer.
Alignment
The alignment of the vehicle being tested does affect the outcome of a dyno test. So if a car is dyno'd, then run over a curb, thus altering the toe or camber, the car may not have repeatable runs. This is especially true on Dynojets.