freedom

As I am sure many of you notice, there is a noticeable diference in performance in my A4 1.8tqms depending on weather conditions. This morning, my car seemed to be running better better than ever. Temp was about 30 degrees out and the engine seemed to run smoother than usual. Same hi-grade fuel as usual and about a 15 minute warm up. I would imagine that the the turbo engines will respond more noticeably to variations in conditions than naturally aspirated engines. The question is: What are the ideal conditions including humidity, temperature, warm-up time etc, and what do these factors contribute to or take away from performance. It is not that my car doesn't always perform and feel smooth but sometimes the engine sounds smoother than others.

Dead

Dry cool/cold air would be the best for any engine , turbo car may feel a more pronounced effect

Dead

I have heard this explained and understand what is being said, but I still wonder. Cool/cold air would still help the IC.

WClark

The key here is charge air temp and air density at the intake manifold.

Everyone knows the turbo heats the air as it is compressed. Obviously if we have colder air in - we have colder air out given a fixed amount of compression which results in a lower temperature air at a given density.

It appears the ECU uses colder outside air temps to reduce the max boost since colder air is already denser. This has a cascading positive effect because we also know the turbos we use have lower and lower efficiency (more heating relative to the increased boost) at higher and higher compression levels, or conversely they have higher efficiency at lower boost. So we take cooler air and compress it less, heat it even less, pass it thru the same intercooler which has colder air passing by it on the outside and voila - MUCH colder air with a given density going into the cylinder. Engines love this stuff - which is why NOS is so effective.

ModifiedA4

Factor in the fact that all the other tubing and other bits are cold and it results in a denser charge of air...Turbo effciency goes up as well since the air has less energy in it when the turbo "sees" it.

freedom

Does humidity have any affect?

ModifiedA4

To keep water in the air it has to have a certain level of energy....Less water= less engergetic air...which means less heated air after compression....

jlai

The energy source in any engine is based on the temperature difference between two system - basic Heat Transfer theory. So if the air temp is lower, the difference of the temp of the turbo and outside is greater and thus more heat ( as a form of energy ) can be transfered and thus more power.

Hope this makes sense.

Thanks