Here's why a Mustang Dyno is more accurate in simulating track conditions than a DynoJet. First, lets all agree on one thing. The rate at which an engine increases RPM DOES matter to tuning (an engine increasing 1000 RPM/sec sees completely different fuel and air demands than an engine increasing at 200 RPM/sec).
That said, the Dynojet uses a fixed weight drum. With the same amount of RWHP, it will accelerate at the same speed regarless of whether you have a 1000# rail or at 5000# heavy street car sitting on it. The dynojet would have you put the same tune on either engine. However, in real life, the RPMs on the 1000# rail increase way faster than the 5000# street car. The rail needs a different tune than the street car.
Now on a Mustang Dyno, the rate of acceleration is controlled by the weight of the vehicle (and perhaps wind speed, I don't know). This will result in a tune that is tailored to the actual RPM increase rate vs an increase rate that is seen when on the dyno.
-Mike
------------------
|