Track Tac

The myth about humidity and its effects on horsepower.

SKHMotorsports71 said:
With all your expert advise you should write a book on dirt oval tires, clone engines, Stagger, ride heights, ect. Please show us the sales volumes when you do write the book!
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I don't think anybody would buy it, I know nothing about dirt oval tires, or clone engines, or ride heights. Most importantly; I never said I did!! I have a spreadsheet that will calculate stagger, but that would hardly fill a book. I don't know anything about kart set up for LTO, but if you give me the corner weights, or the percentages, my spreadsheet can calculate percentages from corner weights or corner weights from percentages. Kind of handy.

Something really handy about that spreadsheet, if you put in the present corner weights in the indicated cells, the spreadsheet will then calculate the percentages. There is a cell right next to the place where you inserted a corner weight that will show the calculated corner weights. If you delete the cell with the calculated total weight, you can then play with the corner weights in the cells that you placed the actual measured weights. By changing the weights you inserted, you can see what will make what change.
 
Just buy a Kestrel 4000 pocket weather tracker and let it automatically adjust the altitude calcs for you. It uses all of the factors from Al's calculator and adjusts density altitude when the factors change. Its with me on every dyno pull I make.
 
Ted Tucholski said:
Just buy a Kestrel 4000 pocket weather tracker and let it automatically adjust the altitude calcs for you. It uses all of the factors from Al's calculator and adjusts density altitude when the factors change. Its with me on every dyno pull I make.
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that's a real nice instrument and the $250 price tag is not all that bad. Still, it's kind of complicated. Tell me why you need all the features the instrument provides for your dyno room. Can you explain how you use it? Does it give you an air density reading? I'm not quite sure how you use a density altitude number.

In my dyno room I had a barometric pressure gauge, a temperature gauge and a relative humidity gauge. This was in 1985. This was along with the water break dyno, the A/D converter, (expensive in 1985) and the control panel. I had custom written acquisition software and charting. I'm pretty sure nobody had a better setup than me.

Today, the data acquisition software automatically adjusts to the ambient conditions, I had to manually enter temperature, pressure and humidity data. You get the same numbers, but automatic is always nice.
 
Density altitude simply has the corrections for your altitude figured in. Obviously on a dyno, the altitude doesn't change, but the air does. These gauges are super convenient for a traveling race team though, where your altitude changes from track to track. Using the same gauge on the dyno as is used in the field is a great idea for consistency. Actually, I regularly ask customers if they would like to send their a/d gauge in with their engine at rebuild time. I gladly place their gauge in our dyno cell at the time I make pulls on their engine. That really helps the customer make better educated decisions on fueling their engine at their track and elevation. Of course, I do my best to figure that into my dyno pulls before shipping the engine to them as well.
I use a Computech gauge to get a density altitude measurement the same way as Ted does with his Kestrel. Technology can be a great aid, and these gauges are a good example of that.



-----
Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
26 years of service to the karting industry
765-339-4407
bcarlson@CarlsonMotorsports.com
 
There is also an app for a iPhone that pulls weather from the closest airport and figures the density altitude. "autodens" is the name of it. Not the degree of accuracy of a handheld weather station obviously.
 
Al, I think Brian answered most of your questions for me. #1. It's no more complicated than your program.#2 I don't need all the features it provides for the dyno room, but they are nice to have. I only need the adjusted density altitude number it provides.#3 you program into the gauge the elavation where you are at. For me I think its 1250 ft, add the current barometric pressure. The gauge reads the temp and humidity, then it takes all that data and calcs the adjusted density altitude. As these factors change in real time so does the calculated altitude. approximately every 333 foot change is about a 1% change in HP.
 
Agreed. 1% per lap here in Phoenix at PKRA equals 4 tenths of a second in the world formula class. Also as far as altitude density here in the summer it can go from 3300 ft in the morning to 4700 ft in the afternoon. Even though it's a dry heat. :)
 
From what I can see in Wikipedia's explanation of air density, I get this; Relative air density is a calculation. Air density is a simple measurement.
http://www.intellicast.com/Local/Weather.aspx?location=USTX0764
go to this webpage and check several cities, at different altitudes, such as San Jose California, (very close to sea level) and Denver Colorado. The barometric pressure at both sites will be very close together, even though Denver is at 5000 feet, because the barometric pressure is corrected to sea level. Airplane pilots need this. I don't really understand all this. I know one thing, (at least I'm pretty sure about this) all you need is the air density where you're at. It doesn't need to be corrected to anything. That's my belief, but I'm willing to listen to counter arguments.

In my manual HP spreadsheet and dyno chart, I put in the actual pressure and the temperature. This gives me a correction factor that is then used in the formula to calculate the horsepower from RPM and torque input.

Send me a set of numbers, (rpm and torque) uncorrected, with the barometric pressure and temperature, and let's see how the horsepower calculation works out between your software and my software. Let's see what the difference is in the horsepower and torque chart.

The point of having correction factors is to give you comparative readings between different places regardless of the barometric pressure and the temperature.
 
Ted Tucholski said:
Agreed. 1% per lap here in Phoenix at PKRA equals 4 tenths of a second in the world formula class. Also as far as altitude density here in the summer it can go from 3300 ft in the morning to 4700 ft in the afternoon. Even though it's a dry heat. :)
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Interesting, and what adjustments do you make between those numbers. Do you know how much change in air density that represents?
 
SKHMotorsports71 said:
Just don't see it...Tires are what will out run that 1/10th!!!
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If tires are more important than horse power then why do people sit on the dyno looking for every 10th that they can get witch is faster perfect tires on a 13hp motor or a 11hp motor with perfect tires I'm not sure you tell me
 
motorhead said:
So who is to say this chart is accurate. I spent many years on the drag strip where HP is always crucial.
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motorhead said:
Motors with high compression {16 to 1or more} didn't suffer as much with barometric pressure.
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Drag cars only have to run seconds, karts have to run minutes.
Worked on drag cars, yeah different.

If anyone here has a clone, Honda, Briggs with 16:1 compression, let them speak now or forever hold their peace. Maybe the UAS crazy guys will chime in...maybe not.

All racing engines share the same physical limitations, some just don't have the cubic inches to give a crap. Drag racing and oval track racing are as much different as the are the same.
Drag engines have a whole 'nother set of challenges that karts don't have. Like the next lap.
 
Somebody should do some flow rate analyses with a flow bench and varying temps / humidities...
Also, I was under the impression that you needed a wet bulb to test humidity...do they have something easier / better now?
 
Steve Vermeer said:
The smaller the displacement and the lower the compression, the more sensitive to changes in weather. Especially grains of water.
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I tried looking it up in Wikipedia with no success. How much is one grain of water?

I'm going on the assumption that at 70° and 70% relative humidity (RH) there are no grains of water in the air. Same with 70° at 80% RH. As a matter of fact, the only time there is water in the atmosphere is when the water vapor condenses into a liquid. Water vapor is something like 700 times less dense than water. Humidity is water vapor, a gas like any other. How much water vapor would it take to weigh one grain? What would be the correction factor for air with one grain of water vapor? I know the HP correction factors for humidity are very very small.
 
kartracer281 said:
If tires are more important than horse power then why do people sit on the dyno looking for every 10th that they can get witch is faster perfect tires on a 13hp motor or a 11hp motor with perfect tires I'm not sure you tell me
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On a dirt oval I will take the very good tires anyday over that 1/10th of a hp!!
 
kartracer281 said:
Im just saying that you can add 10ths of a hp it adds up
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Sure it does on a sprint track or a very large oval but on an 1/8 mile oval or smaller I will take perfect tires over a 1/10th of a hp all day long...the 13 hp to 11hp is not even a fair comparison and should not even be considered as we were speaking in a 1/10th of a HP not 2 whole HP!!

And No AL I did not miss the point!

JMO Not everyone in the race is going to be on perfect tires! lol It would be a very rare occurence if they were!
 
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