i found this info from another site and thought i would share:
Mods can we perhaps sticky this?
Ok I'm going to supply some information based upon my 13+years of working with chassis dynos. I'm going to keep this as factual as possible w/ as little bias as possible, I invite any of the other dyno reps to posts or shop owners who have a dyno.
First off I will state my current position. I am the southeastern USA sales rep for Dyno Dynamics. In the past I have worked w/ dyno from various mfgs. All of these dynos I have had extensive experience with. Dyno Dynamics, Dynojet, Superflow, and Mustang. I have working knowledge of Roto-Pak, Dyna-Pak, Bosch, and Maha.
This is key, an number is just that, a number.
It doesn't matter wether a dyno reads 400hp on 1 mfg's dyno or 3 apples, 2 oranges, and a kumquat on some other mfg's dyno. A dyno is a tuning tool. The purpose of a dyno is to simulate real world conditions to help tuners. What is important is to see how change made to the vehicle affect it's power output. So your tuner makes a change and now you make 405hp or 3 apples, 2 oranges, and 2 kumquats.
A gain is a gain, a loss is a loss, period.
Numbers are only good for pissing matches and bench racing.
Now on to the comparison:
Here is how the various mfg dynos relate to one another. This is just a comparison of numbers output assuming the same vehicle on the dyno.
The industry leader in number output by far is Dynojet. Their marketing in the mid-90's specifically used the larger output numbers as a selling item.
Next is Mustang, generally about 7% less than Dynojet numbers.
Superflow is about 3% less than Mustang.
Dyna-Pak and Dyno Dynamics are about 3% less than Superflow.
Ok lets make this point again to make sure it's clear. The SAME CAR on the DIFFERENT DYNOS. So our test vehicle output on the various dynos are as follows:
Dyno Dynamics 200hp
This is assuming the dyno operator has not changed any of the parameters of the dyno. All of the dynos software incorporates parameters that are operator definable. These adjust the displayed power output. In other words the operator can "adjust" the output of the dyno to display any number desired. By adjusting weather station parameters, external corrections factors, inertia compensation, or any one of a dozen different factors the output number can be modified. The number can be modified to display anything from 10% of measure power to 300%. So our 200hp example vehicle can after a pull display peak power of 20hp or 600hp w/ just a couple of keystrokes.
Key Fact: Just because the dyno spits out a number, it doesn't means squat without knowing ALL of the correction factors.
Some dyno operators adjust the output of their dynos to closely match the highest numbers in the industry, Dynojet. This is not an attempt to defraud the customer. It is just that customers have a false notion that a bigger number means more power. But as you have seen, numbers mean nothing.