There is no simple answer to this, we warn everyone before coming to us for any services. The best description I have found online is quoted next....

" I have traveled this country for years tuning cars on dynos. I bet I have more dyno experiance then just about anyone. THis is my ranking from highest to lowest reading dynos:

1. Dynapak hub dyno.
2. DTS Dynamic test systems
3. Dynojet
4. Dyno dynamics (old software read low, Owners complained, New software reads high)
5. Mustang AWD 500 series.

Dynos can be altered. I know of a few shops who have altered the machine or the software to have higher numbers. They are on these forums. Its clear who they are. Remember. These people are in this to make money and to eat. They sell more parts and ecu's and services when numbers are higher. This flat out sucks for the honest guys because our dynos read "low". I am one of those guys. I tune each day on a low ass reading Mustang AWD 500. I have to explain just about everyday how you cant make 400 fricken wheel hp on pump 91 in the 115 degree heat with an fp green. You make 330 and be happy the car is tuned right

Clark"