App for atmospherics?

[ArizonaGuy]

What do y’all use for atmospheric mobile apps?

[Mummert]

"Air density online" works good for people without a weather station.

[David Redszus]

A weather station is useful to determine relative humidity, and little else.

Inlet air temperature and inlet air pressure, along with humidity, are necessary
to calculate air density.

We have measured 30 degree air temperature change during a race.
Inlet air density will also change with rpm and vehicle AIR speed.

[xxdabroxx]

I've been using "Drag Racing Weather" for android. It's OK, but not great. Sometimes it fails to update the weather data.

[pcnsd]

What are you looking for in output?
1. Relative air density as a percentage.
2. Air density lbs/ft3
3. Air density kg/m3

[Mummert]

A weather station is useful to determine relative humidity, and little else.

Inlet air temperature and inlet air pressure, along with humidity, are necessary
to calculate air density.

We have measured 30 degree air temperature change during a race.
Inlet air density will also change with rpm and vehicle AIR speed.

Tools are tools. Its a racers job to make sure the engine is getting good quality air and jet the car through the course of the day. Good weather stations have software to predict E.T changes as the air changes. Every car will have its own coefficients of underhood temp and pressure rise based on many different factors. A good racer will be be able to compile information and develop trends and be successful.
Air Density Online works well for guys who have nothing, it also can teach people how the air changes through the day, how more humid days see less change in DA then dry days. Give people an understanding of Uncorrected Barometer and its direct correlation with altitude and Corrected Barometer and its correlation with a particular regions high and low pressures. I actually use it the more for predicting a day or so ahead so you can do a baseline jet at home so your not wasting time and runs at the track. Using whats available in conjunction with your other tools on hand has proven helpful to me.

[ChopperScott]

http://www.dragtimes.com/drag-racing-ca ... -tools.php

[David Redszus]

The density of the air that goes into an engine is determined by inlet pressure, inlet temperature, and humidity.
It cannot be determined by a weather station of any kind, although a knowledge of probable weather conditions
at a track before arrival does have some value.

Densitty Altitude also has no value in density determination; it can only provide an approximation.

Changes in inlet temperature, inlet pressure, and humidity will affect not only air density, but
also air viscosity which will impact inlet air flow.

Drag racers often feel that underhood changes will have little effect due to the limited run time.
But oval track and endurance road racers can be substantially impacted by changes in underhood conditions.

Consider starting conditions of 14.7 psi, 80F deg, and 0 RH; density is 1.177 kg/m3 and viscosity is 0.0187 cP.

Then:
15.2 psi = 1.217, vis = 0.0187cP
15.7 psi = 1.258, vis = 0.0187cP

and
90F = 1.155 = 0.0189cP
100F = 1.135 = 0.0191cP

and
40 RH = 1.162, 0.0187cP
80 RH = 1.146, 0.0187cP

An increase in pressure will raise inlet air density.
An increase in temperature will reduce inlet air density and raise viscosity.
An increase in RH will reduce inlet air density.

Clearly, all three parameters can vary simutaneously; what then are the resulting values
for air density and viscosity?

And...what effect do they have on engine jetting and power production?

[pcnsd]

The density of the air that goes into an engine is determined by inlet pressure, inlet temperature, and humidity.
It cannot be determined by a weather station of any kind, although a knowledge of probable weather conditions
at a track before arrival does have some value.

Densitty Altitude also has no value in density determination; it can only provide an approximation.

Changes in inlet temperature, inlet pressure, and humidity will affect not only air density, but
also air viscosity which will impact inlet air flow.

Drag racers often feel that underhood changes will have little effect due to the limited run time.
But oval track and endurance road racers can be substantially impacted by changes in underhood conditions.

Consider starting conditions of 14.7 psi, 80F deg, and 0 RH; density is 1.177 kg/m3 and viscosity is 0.0187 cP.

Then:
15.2 psi = 1.217, vis = 0.0187cP
15.7 psi = 1.258, vis = 0.0187cP

and
90F = 1.155 = 0.0189cP
100F = 1.135 = 0.0191cP

and
40 RH = 1.162, 0.0187cP
80 RH = 1.146, 0.0187cP

An increase in pressure will raise inlet air density.
An increase in temperature will reduce inlet air density and raise viscosity.
An increase in RH will reduce inlet air density.

Clearly, all three parameters can vary simutaneously; what then are the resulting values
for air density and viscosity?

And...what effect do they have on engine jetting and power production?

Similar to Mummert Machine, I use a sheet to prepare for race day jetting changes based on a tuning day jetting standard, expected conditions and changes to relative air density. I do not consider air viscosity in my jetting change calculations. I mostly see seasonal temperature swings and have raced from the mid 40F to 108F. Practically speaking, in a carburetor application, how much difference does viscosity make to jetting? Can you recommend a resource to understand its calculation? I seldom change anything other than the main jet and adjust the idle fuel screw. If changing the mid-range jetting has a practical effect... I cant tell.

RAD jetting.PNG

[David Redszus]

When we refer to changes in atmospheric conditions, we do not simply mean the weather
or conditions indicated by any weather station. We mean changing conditions affecting
the absolute air density that enters the engine and is available to burn supplied fuel.

Changes in track location often involve elevation or altitude changes.

Holding temperature and humidity constant, a change from sea level to an elevation of 1200 ft
will cause a change in air density from 1.186 kg/m3 to 1.126 kg/m3.
This change in delta pressure will reduce density by 5.08% and require a change in
fuel mass of 5.08%, resulting in a power loss of 6.06%. A power loss that is non-recoverable.

But, conditions can also change during a race. Holding altitude and humidity constant,
an increase in inlet air temperature of 20F deg will result in a density loss of 4.14%,
decrease in required fuel of 3.17% and a power loss of 1.87%.

For optimal performance, we must consider dynamic conditions which include
throttle position and rpm, which will affect inlet air density.

The best tool currently available is a Lambda sensor coupled to a data logger
to monitor TPS, RPM, air density, and mixture while on track.

[RDY4WAR]

I used to not monitor intake air temps until it bit me a few times. My ram air is sealed to the front bumper which is just 3-4" off the ground. I didn't realize how much the heat coming off the track surface was affecting air temps. Per the weather station, the water grains dropped and barometric pressure increased slightly with the same temperature so I was expecting the car to run a little quicker than the previous round. I dialed accordingly. Nope, the car slowed a few hundreths. The next weekend, the same thing happened. That's when I made the connection to the sun hitting the track.

After installing an intake air temp sensor, I've observed it once since then. Ambient temperature dropped a couple degrees with a drop in humidity but my intake air temp was >10°F hotter. Now when I'm 2-3 pairs from the start, I have my buddy go check the track temp before I set my dial-in.