Ok, first.... so cold air going into the car is good for performance. Does that mean that cars have better HP/performance in the winter time?

Next, how come when you dyno a car that you don't do it in a wind tunnel to simulate true airflow?

 

Not sure, but because the car is not moving,the air flowing over it has no effect,unless it was blowing hard enough to push it off the dyno
Don't know about HP but MPG drops when the temp falls below -20.At -40,yes some of us motor at that temp ,my highway MPG drops by about 20 %
But I'm toasty with the heat on defrost and the cosy heated seats on

 

In any colder environment if all other factors are equal then yes the colder air is more dense and that helps with performance. More HP with colder air.

However if in the winter you have icy slick roads then that doesn't help.

Figure it's nice out on a clear but cool 40 to 60 degree day in the spring or fall.

With a dyno you are trying your best to simulate real driving and air cooling the front of the car, but even with large fans you can get only so much airflow. The dyno is only an approximation of measureable power. The relative number is then used to make comparisons but it isn't as accurate as one might think since there are so many variables.

Too bad in Hawaii we don't have many of those cold days. No ice on the roads at sea level so that's a plus.

 

As a matter of fact, most engines, especially intercooled ones, do perform better in the winter/colder months. Tires tend to perform less well in the cold, since many of the stickier compounds like to have some heat to work their best.

Most dyno testing uses some form of forced air into the intercooler and radiator in the form of fans. Many cars will overheat during repeated dyno pulls because their cooling systems were designed with vehicle-in-motion airflow in mind when under load.

A Cooper S (or any similar vehicle) which uses in-motion airflow to cool the intercooler needs some form of forced air during a dyno run or the results will be invalid. In fact, you need a rather serious fan (not a 20 inch window fan) to simulate the in-motion airflow.

 

Well maybe no ice at sea level where you are minihune,but on our left coast,
they can get bad ice on roads even at sea level.Now those of us that live were there is real winter,we take great delight watching those in B.C. play bumper cars when they get their one day of winter.

 

I realize that most, if not all, dyno tests are done with fans or forced air movement. But I'm talking a true wind tunnel. Where you can simulate the effects of wind at 55+ MPH. Like those aerodynamic tests with the smoke trailing over the car.

Maybe my lack of dyno machine knowledge is lacking, but seems to me that jet engine testing is also done in a wind tunnel.

 

THere is no need to do a dyno run in a wind tunnel environment. Unlike aircraft engines, auto engines are not very affected by airflow over the vehicle. A jet engine needs (expects) a large flow of air coming at it when in operation, and this affects it's operation directly. Dyno testing the car in a wind tunnel will only introduce a force trying to push the car off the rollers. When driving, resistance to vehicle motion is caused by friction, hills and aerodynamic drag. In the case of drag, that's a constant. Tunnel test a vehicle once to get a drag coefficient (this does not change with horsepower, engine type, etc) and you are done. Unless you substantially change the vehicle's aerodynamics, there is nothing that will overtly change the vehicle's performance. From the dyno you will know the horsepower at high speeds, factor in the drag coefficient and you can mathmatically determine the acceleration and top speed of the car.

A good dyno setup will have a fan capable of blasting the front of the car with a breeze equivalent of 50mph or better to allow the intercooler to function well and keep the engine temps down to get the best idea of the true horsepower of the setup.

 

Crispy claer blue sky days are referred to as "Horsepower days" at the track, not so much for the coldness as for the fact that a clear blue sky is a sign of high atmospheric pressure. More pressure=more air into the cylinder=leaner combustion=more energy release= more force moving the piston down (or the rotor sideways). All things being equal.....cold air=more HP.

A dyno measures torque. torque is the physical force needed to move an object or to stop an object. a rolling dyno measures the torque the wheels exert to get the big *** rollers going and then HP is calculated. Dynos do not measure speed, and the car's speedometer is giving you wheel speed, not true speed (ats the true speed is zero)
Hope this helps....