Temperature and Air Volume

Discussion in 'Motorized Bicycle General Discussion' started by CTripps, Nov 19, 2011.

  1. CTripps

    CTripps Active Member

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    I was thinking about how my motor performed on cool mornings compared to warmer afternoons the other day, and got to wondering about the effect of temperature on volume with regards to air volume. I figured I'd throw it out here for anyone else who might have had an idle thought about it. Warmer air is less dense, so lower volume, etc. I figured the differences would probably be very minor. At Engineering ToolBox I found this information. They also have information regarding the effects of altitude and more. Granted, if I've done the math right it doesn't look like a lot until you look at the mornings where it's chilly or closer to freezing compared to a normal daytime temperature or a hot day. I didn't do the math all the way down past there, but did the extreme end to see where it ended up. I'll leave that to others to test, I'm not that dedicated to riding. ;)

    Anyway, yeah the difference isn't huge. I'm possibly 'gaining' 4cc or 6% or so worth of power in the mornings. We haven't been near the 22°C '0.0' here for a while. Haven't seen it here, but where I used to live we had plenty of days with frost on the ground in the morning and hot afternoons.

    Sorry about this mess, I can't get a table layout working for me:

    Air_________| Volume___| Effect on
    Temperature_| Correction_| Air Volume
    (°C)__(°F)___| Factor____|

    49 | 120 | 1.10 | 66cc = 60cc
    43 | 110 | 1.08 | 66cc = 61.1cc
    38 | 100 | 1.06 | 66cc = 62.2
    32 | 90 | 1.04 | 66cc = 63.4cc
    27 | 80 | 1.02 | 66cc = 64.7
    22 | 70 | 1.00 | 66cc = 66cc
    18 | 60 | 0.98 | 66cc = 67.3
    10 | 50 | 0.96 | 66cc = 68.75cc
    4 | 40 | 0.94 | 66cc = 70.2cc
    -1 | 30 | 0.93 | 66cc = 70.9cc
    -5 | 20 | 0.91 | 66cc = 72.5cc
    -9 | 10 | 0.89 |
    -18 | 0 | 0.87 |
    -23 | -10 | 0.85 |
    -28 | -20 | 0.83 |
    -34 | -30 | 0.81 |
    -40 | -40 | 0.79 | 66cc = 83.5cc
    -46 | -50 | 0.77 | 66cc = 85.7cc


    Numbers from Engineering ToolBox

    Page link: Air - Temperature and Volume
     
  2. Allen_Wrench

    Allen_Wrench Resident Mad Scientist

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    Ya know, I've had to ride my bike home from work when the temperature had jumped to 110 that summer here. And she was laboring on the hills. I could tell.

    And I've ridden her on brisk 40 degree mornings, and she felt like she could kick butt and take names. I thought all along that air volume might play a part. This kind of supports my theory. It looks like there was almost ten cc of difference between those times. Thanks for the info.
     
  3. happyvalley

    happyvalley New Member

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    Makes sense. My little 4 strokes just seem to purr when it's 40 to 50 degrees out.
     
  4. scotto-

    scotto- Custom 4-Stroke Bike Builder

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    Too bad we can't inject dry nitrogen in to our engines like we can our tires.....

    dnut
     
  5. maintenancenazi

    maintenancenazi New Member

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    ^^ If I remember correctly, someone tried this many years ago. This was on a small block chevy I believe. They basicly connected there AC output to the air cleaner intake, in theory making there engine "think" it was winter. It was a dead end though, being that any gains in HP were lost due to parasitic drag from the compressor.

    But yea, colder air can make a huge difference in power, most pronounced if you richen your jetting to compensate for the now denser air.
     
  6. CTripps

    CTripps Active Member

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    That's sort of what got me thinking about it. It's getting colder here now and the motor was just loving the morning air, fired up quickly every day and seemed to have more response to the throttle. You're only looking at 5-7% more or less air either way for most riding but it's noticable.

    I'd think after looking through some of the other pages at the Engineering ToolBox site regarding air density by altitude etc would yield similar, seemingly low percentage differences. I didn't, since I'm close enough to sea level but I know if I took my bike up to somewhere a couple of thousand feet over sea level it wouldn't run worth a $#|+ until some adjustments were made.
     
  7. bairdco

    bairdco a guy who makes cool bikes

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    here's something of interest i picked up from a 2 stroke performance site:

    Cool Fuel - Keep your fuel can in the shade, better yet, pack your fuel can in ice. (You can use the empty cooler since you and your friends drank all the beer the night before). As fuel vaporizes in the carburetor it has a cooling effect on the incoming air. Cooler air is denser and has more oxygen, the cooler the fuel is when it vaporizes the cooler the air will be and the more power it will make, plus the engine will run cooler also. In drag racing it is common practice to run the fuel line through a canister full of ice. Also the fastest drag race times are run on cold days because of the denser air.
     
  8. Maxvision

    Maxvision New Member

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    Wondering if humidity might be a factor to consider?
     
  9. F_Rod81

    F_Rod81 Dealer

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    There are all sorts of weather factors the play with it though. Since you live in SoCal you probably won't notice the humidity factor like I do in Colorado. I can feel the humidity factor come into play when I ride on the bike paths next to the rivers. There is room for debate whether gravity plays a factor as well. Although the effect would be extremely small, you never know; A way to determine this is compare night riding to day riding.
     
  10. CTripps

    CTripps Active Member

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    Dry air is more dense than humid air, so probably. Again, I would expect the results to look minimal but be noticable. Take a look around the site I mentioned above, I've seen links for that as well.
     
  11. Allen_Wrench

    Allen_Wrench Resident Mad Scientist

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    There's something you could try for the Deathrace, Bairdco: chillin' your fuel. And heck, copper fuel line would be perfect for strapping a chilled gel freezer pack onto. Ya know, that may actually work. Whatcha think?
     
  12. bandito

    bandito New Member

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    Why isn't particulate matter figured into this equation?
     
  13. Jumpa

    Jumpa New Member

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    mY MUSTANG DOES THE SAME THING COOLER DAYS AND OR IN THE RAIN COME TO FIND OUT IT HAD TO DO WITH A SLIGHT BIT MORE OXYGEN IN THE AIR WHEN IT RAINS
     
    #13 Jumpa, Oct 3, 2013
    Last edited: Oct 3, 2013
  14. maniac57

    maniac57 Old, Fat, and still faster than you

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    Cooler denser air improves power in any engine. You just feel it more with these marginal china girls. Mine all respond big time to fall weather conditions with much peppier performance and better mileage.
    I'd say the difference between 90deg days and 70deg days is at least 1hp...minimum!
    Maybe quite a bit more depending on your particular jetting and setup...
     
  15. 2door

    2door Moderator
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    Ask any pilot what he thinks about 'density altitude' and aircraft performance. As for humidity, they injected water into the carburetors of WWII fighters to raise the compression/horsepower of the engines. Google, 'water injection'

    Altitude above sea level will play an important part in carb jet selection. The higher you are, the smaller the jet needs to be to compensate for the less air density.

    I know this is an old thread but Maniac bumped it. I just added a little food for thought.

    Tom
     
  16. xseler

    xseler Well-Known Member

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    Higher humidity = more water.

    Rapidly heated water = steam.

    Steam = more power.


    Hope y'all enjoyed that scientific 'planation! :D
     
    #16 xseler, Oct 3, 2013
    Last edited: Oct 3, 2013

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