Originally Posted by Andrew@ActiveAutowerke
A fan blowing directly on the filter will skew the results of this test. On the street will it get forced more air and make this power? Its very possible!
On the road the air is also most definitely less polluted (assuming your not driving behind some dirty derv truck) and it's proper ambient temperature.
Dyno cells tend to be higher than ambient and exhaust gas recirculation really takes effect which doesn't help.