Originally posted by siueclipse
A car will reach its hp no matter what the outside conditions are. It might take it awhile to get to the high horsepower if you take into effect things like drag or wind. In most cases, because of putting a load on the motor, motors tend to perform better or work harder as well. What about colder air rushing into an intercooler? Doesn't that make power or are intercoolers a waste of money?

If weight and load did not matter than you could run the exact same time at the track whether your car was empty or if you have four people in it. When your not on a dyno your pulling a car vs turning rollers. The dyno does it's best to replicate this environment but dyno jet dyno's are not famous for being the most accurate at this. As for the cooler air, that is what the fans at the dyno are for. Yes you might get more airflow on the open road but the results are not going to be that much greater than a decent cooling fan setup at a dyno. Not to mention the fact that you dyno with your hood open so your releasing a lot of heat that way as well.