Need some help please

alvin l nunley

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http://wahiduddin.net/calc/cf.htm
there's a formula here for calculating air density.
I made a very simple dyno sheet for calculating HP. You put in your torque and rpm numbers and it calculates the horsepower. Also there's a chart. Shows horsepower and torque.
At the URL above, there is a formula for calculating air density that I can't make hide nor hair of. My math skills are limited. The formula is a graphic and will not transfer to here.
I have the air density calculation in cell A5. The barometric pressure number is in cell E3. The temperature is in cell G3. The temperature converted to Celsius is in cell E74.
If anybody can help me with this I sure would appreciate it.
 
i see 2 equations for calculating Correction Factor (cf), but don't see one for calculating Air Density?
 
Alvin, forgive me for being even dumber, but I see your post topic that asks for some help, yet I don't see a question in your post. Though it does read like you want help with a way to calculate air density.
What do you want help with?
 
Alvin, forgive me for being even dumber, but I see your post topic that asks for some help, yet I don't see a question in your post. Though it does read like you want help with a way to calculate air density.
What do you want help with?
if you go to the link that I published in the 1st post, scroll down and you'll see formula for computing a HP correction number. The calculations require metric numbers. I don't have the metric numbers. I have the barometric pressure cell and the temperature in Fahrenheit cell. If I could convert the formula to use my information it would be great. Converting Celsius to Fahrenheit it easy. Converting the pressure number is harder. Converting, let's say, 29.27 on a standard barometric pressure gauge, whatever they call that, to millibars, is harder.
I appreciate the interest.
 
Here's a sales pitch for airdensity gauges about why.
I appreciate your input Paul, but I'm not trying to calculate air density in the way you are taking it. There is a formula for calculating the correction factor for horsepower. The formula needs to temperature in Celsius, which is easy to convert to Fahrenheit, but it wants the pressure in millibars. At that point, I'm lost. lol
 
I appreciate your input Paul, but I'm not trying to calculate air density in the way you are taking it. There is a formula for calculating the correction factor for horsepower. The formula needs to temperature in Celsius, which is easy to convert to Fahrenheit, but it wants the pressure in millibars. At that point, I'm lost. lol

That's what I suspected, but your wording threw me off. The equation is asking for Dry Air Pressure, so i believe it is more than just a simple units conversion. Its been a while since I have done any pressure calculations. There is a link on that page to the page below that I think might help explain some of it, but it gets kinda complicated.

http://wahiduddin.net/calc/density_altitude.htm
 
That's what I suspected, but your wording threw me off. The equation is asking for Dry Air Pressure, so i believe it is more than just a simple units conversion. Its been a while since I have done any pressure calculations. There is a link on that page to the page below that I think might help explain some of it, but it gets kinda complicated.

http://wahiduddin.net/calc/density_altitude.htm
I believe it's asking for dry air pressure to rule out any effect humidity would have on the calculations. The correction factor for humidity is so little, I don't think it's a consideration. I'm just going to put in what the barometer says at the moment, dry air or not.
 
Al, the US unit of measurement for barometric pressure is inches of mercury. Inches of mercury multiplied by 33.8637526 will give you milibars.
 
At my altitude @ 10,000 , I can run a motor on the dyno and find the best tuning for it to run it's best at this altitude and get real time and/or Corrected Factored results.
Yet I don't use it because it's pretty much meaningless to find the perfect tune for a motor running at 10,000 ft. when I want to race it and find the perfect tune @ 4,000 ft. instead.
I would like a climate controlled dyno room, yet for it to be controlled well would be a hard process and any out of control would be more like tuning a turbo charger.
 
Alvin I think what you want is 1 inch of mercury equals 33.86 millibars, so....standard barometric pressure at sea level is 29.925 inches of mercury OR (29.925 X 33.86 = 1,013.2605 millibars). Maybe this will help find what you are looking to figure out.
 
=(1.18*(((990/E75)+((E74+273)/298)*0.5))-0.18)
this is what I have so far. Trust me the cell references are correct.
One thing I'm wondering about is the *0.5. In the original formula from the 1st post I see the 0.5, but I'm not sure that's a multiplier. It could be a power.
E 75 is 1015.971 as in 30 inches of mercury expressed in millibars.
E 74 is Fahrenheit converted to Celsius.
 
Yes the .5 is an exponent. Use the "^" symbol.

You also have an extra set of ().

=(1.18*((990/E75)+((E74+273)/298)^0.5)-0.18)
 
Yes the .5 is an exponent. Use the "^" symbol.

You also have an extra set of ().

=(1.18*((990/E75)+((E74+273)/298)^0.5)-0.18)
thank you so much for your help. My horsepower chart now has a correction factor in the calculations. I checked it against the online correction factor calculator and they both show the same correction factor. Yahoo.
 
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