My bad, I thought people might be interested in picking up the article to read! It really is about the best article I have seen on the topic. I bought the mag to send to my son in Iraq for reading material, so I don't have it in front of me anymore, but some notes from memory.....
Dynojets are the most optimistic dynos, generally showing 8-15 HP more than dynos like the Mustang which are considered more accurate. However Dynojets are more consistent from unit to unit, so are best for comparing results from different dynos. They are also less prone to improper setup and maintenance and the results are not as easily 'adjusted' by an unscrupulus dyno operator. They took a mustang car around and ran the same car on 4 or so different styles of dynos and showed the results.
Lower gear ratios do cause the dyno to read a little lower on power both for the increased system losses (true HP loss) and due to the way the dyno takes it's readings. The physics of this escape me at the moment but seems to have to do with the inertial type dynos like the Dynojet. Don't think it was much, perhaps 5HP or so. By the same logic, they said smaller diameter tires will show lower HP than larger ones since they also affect the final drive ratio.
The way the car is strapped down to the dyno can also have a fairly large affect on the reading as well. They mentioned how just changing the straps by 1 click could affect HP readings by X amount.
--- Ken
