2. There are no rolling roads that can properly simulate the airflow normally achieved on the open road through the intercooler and radiator. Proper cooling simulation would require a moving floor and variable speed fans (as found in professional wind tunnels). Some rolling roads do a better job than others, using high-powered centrifugal fans. Others just have a single axial flow low-pressure unit. On occasion this is just aiming at the intercooler and not. producing flow through it. Proper flow through the intercooler is critical in order to simulate normal running conditions a 10 degree increase in charge temperature can cause a considerable loss in power

5. Most rolling roads "correct" the measured bhp to a din standard for atmospheric pressure and temperature (and some don't bother!). The purpose of this correction factor is to allow for example a comparison between a five deg C winter day power run and a 25deg C summer day power run. The cooler air in winter being denser will (all else equal) produce more power than the 25 degree summer air. The din calculation compensates for the different air density and corrects all results to reflect what would have been achieved on a standard temperature and pressure day. This correction works well on normally aspirated cars but is inappropriate to turbo charged cars.The rollers which do not compensate are likely to read high results in winter and low results in summer. The din calculation looks at only air inlet temperature. There are however, two temperatures that affect a turbo cars output - air inlet temperature at the filter intake and air temperature after intercooler (charge temp) The air temperature at the filter does not affect the turbo car in the same way as it does in a non-turbo car. This is due to the turbochargers ability to partially compensate by spinning faster and still compressing the same amount of air regardless of temperature. There is however, a price to pay for this in increased exhaust gas back pressure and higher turbo discharge temperature which is dependant on density recovery in the intercooler. The air temperature after the intercooler will normally be higher on a rolling road due to the reduced cooling airflow. Depending on the ECU this may or may not be compensated for in the fuel and ignition maps. Power output will be reduced as a result. It is not uncommon to see a 40 degree c rise in charge temperature on a rolling road run. This is not compensated for within the rolling road software. Some ECU's have there own internal compensations to adjust boost pressure in relation to atmospheric pressure and temperature. This also is not considered in the rolling road din correction factor.