question about coldness

[robcarync]

so if cold air is more dense and leads to better combustion in the engine...(IE cold air intake)...why do the winter months decrease performance in our cars? when it is super cold...wouldnt that lead to the normal air getting more dense and better combustion in the winter?

maybe tis a paradox?

[1996 328ti]

Different formulation of gas?

[barische]

mor cold air u get then the comp sends more fuel in to the engine which results in lower gas milage but more hp.

[ZeroG]

mor cold air u get then the comp sends more fuel in to the engine which results in lower gas milage but more hp.

Cold Air normally does equal moer power to a point. It is possible to surpass that threashold by reaching temperature so cold, that you have gone beyond the ideal performance conditions.

-Chad

[barische]

what he said

[mickd]

I notice a substantial increase in power on cold, dry days in winter. Seat of the pants says around 5-10 HP more than a 70 degree day. I think the key is cold and dry, water is compressible.

[ZeroG]

I notice a substantial increase in power on cold, dry days in winter. Seat of the pants says around 5-10 HP more than a 70 degree day. I think the key is cold and dry, water is compressible.

As far as I know water is not compressible and that is why when using Water Injection with an FI car and injecting before the blower you will see a loss in Boost. You are replacing air with water.

-Chad

[mickd]

As far as I know water is not compressible and that is why when using Water Injection with an FI car and injecting before the blower you will see a loss in Boost. You are replacing air with water.

-ChadI was always under the assumption that water was compressible, it is, but nowhere near the extent air is. Why is it then that it seems like there is more power on a cold, dry day than cold and humid? I know water injection is used to prevent detonation, mostly seen on drag cars with superchargers that have extremely high (effective) compression ratios that come from high boost levels.

[ZeroG]

I was always under the assumption that water was compressible, it is, but nowhere near the extent air is. Why is it then that it seems like there is more power on a cold, dry day than cold and humid? I know water injection is used to prevent detonation, mostly seen on drag cars with superchargers that have extremely high (effective) compression ratios that come from high boost levels.

The answer is in what you said above.

More power on a "cold", "dry" day. And less power on a "cold", "humid" day. When the humidity in the air is less, there is less water in the air. Cold Air is more dense, and when it is dry (less humidity) there is less water and it is more dense. Which makes the car have more power.

-Chad

[mickd]

I did a bit of research and also spoke to a co-worker and friend who is a helicopter pilot and found out that even though water is much more dense than air on its own, water vapor is not. I am not going to say oxygen for "air" because are many more gases present in air than just oxygen. Air consists mostly of Oxygen and Nitrogen. The atomic weight of a molecule of oxygen (O2) is 32. Atomic Weight of a molecule of Nitrogen (N2) is 28. Now, a molecule of water vapor has an atomic weight of 18, consideribly less than the O2 and N2. This water vapor dilutes the dense mixture. My pilot friend says the rotors effciency is greater in lower humidity air (more dense).

[mickd]

I notice a substantial increase in power on cold, dry days in winter. Seat of the pants says around 5-10 HP more than a 70 degree day. I think the key is cold and dry, water is compressible.What I meant to say is water vapor is more compressible.

[GDB]

the primary factor in humidity is that water is not combustible, therefore it is taking up space that combustible air would usually be occupying. Since it is not compressible then it increases the compression ratio SLIGHTLY, but it is not enough to make up for the loss of combustible material.

[mickd]

the primary factor in humidity is that water is not combustible, therefore it is taking up space that combustible air would usually be occupying. Since it is not compressible then it increases the compression ratio SLIGHTLY, but it is not enough to make up for the loss of combustible material.Like I said, water vapor (humidity) dilutes the air. And water vapor IS compressible. Like you said, this water vapor is not combustible and taking up space air would normally be occupying (when the air is dry).

[robcarync]

alright thanks everyone! those are interesting answers i would have never thought of!