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Thread: Cool dense air in the morning

  1. #1
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    Cool dense air in the morning

    Awhile back the topic came up, how well or not cool dense, water vapor air makes an engine run. Not that it matters except it's still on the mind. And water injection since the '30's was a way to increase performance in piston fighter aircraft.

    Back in the day, Missoula '84 if the memory's correct, at a guru seminar, it was commonly agreed that the early morning water vapor air made an engine really run good because of increased density, and the water.

    It just crossed my mind this morning as the bacon sizzles, maybe a comment or two from some experts, for fun. Once I saw a guy with a homemade system rigged up on his VW.

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    Never mind, I just Wikipedia'd the topic and was surprised to find such water injection systems on varied applications from military and commercial jet aircraft to the turboed Olds F-85 and Saab 99. I guess water in the tank or float bowls doesn't qualify. Can't wait for the next cool foggy morning.

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    You know, I have to admit, that my '78 R100/7 ran MUCH better early in the morning especially better when it was cool and foggy.

    Years ago, at the amateur auto drag races some of the racers, between heats, would put dry ice on the intake manifolds and kept the gas cold. They claimed that the fuel flowed better and burned better. I am not sure if it was a fad or some cockeyed idea.

    However, every time I take my bike out in early morning, with cool temps and foggy, it really seemed to run great and smooth. Probably my "cockeyed" imagination!

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    A friend had a '63 Olds F-85 with the aluminum 215 no turbo, which was like a Mustang before the Mustang. The small block Olds turbo engine actually, according to wiki, could use something called "turbo-rocket fluid."

    When it's raining and my ride (commercial) is full throttle down the runway at takeoff, and my partner is worried about the rain, I tell her the engines love the dense air. It's my experience too, that on a particularly cool damp morning that my airhead really honks on the gas. Maybe it's the fog restricting my vision rather than speed that gives me the feeling?
    Last edited by 8ninety8; 11-22-2013 at 10:08 PM.

  5. #5
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    Cool Dense Air

    Every bike I ever owned ran much better in the rain. The engine runs so well that, solo in no/light traffic on straight roads, you tend to speed up rather than slow down. It's not just me, ask your buddies.
    Last edited by 13278; 11-23-2013 at 02:20 PM.

  6. #6
    Registered User widebmw's Avatar
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    I learned that from "Maybelline"

    The Cadillac pulled up ahead of the Ford
    The Ford got hot and wouldn't do no more
    It then got cloudy and it started to rain
    I tooted my horn for a passin' lead
    The rain water blowin' all under my hood
    I knew that was doin' my motor good

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    Registered User chewbacca's Avatar
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    Back in the military we had this saying "don't sweat the small s--t." IMO, that's what this is. There is one heckuva difference between FULL Military Power on a WWII piston fighter shooting alcohol and water into an engine and the effect of humidity on a boxer. I would bet there would be more impact on what fuel package you were running. I know my GS runs better on mid-grade non-ethanol.
    Old But Not Dead
    Semper Fi

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    Humidity can increase power if you can make adjustments for it. It does decrease efficiency. You have inert matter with a fairly large heat capacity in the combustion chamber absorbing heat. These are combustion engines not steam engines. The harder you slap the piston without damage the more power you make, but it might not feel smooth.

    That said I also love the feel.

    Rod

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    Geoxman KJ6OCL's Avatar
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    My R12C really jumps on a cool misty day! Fuel economy on my diesel PU is significantly increased on cold rainy days. There was a time when some guys used to feed small amounts of water into the intake manifold from a reservoir. It's all good.

    Lkarl KJ6OCL / 2000, R1200C

  10. #10
    not so retired henzilla's Avatar
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    too dense?
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    Steve Henson
    SABMWRA MOA Club#62's Flat Fixer/ current forum moderator
    It's not the breaths you take, but the moments that take your breath away-D.Dillon/G. Strait

  11. #11
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    Quote Originally Posted by henzilla View Post
    too dense?
    It just doesn't get any better!

  12. #12
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    It's not necessarily for power...

    A long time ago, I was an aero-engine tech, working on RCAF Argus. The Argus was an anti-submarine aircraft with 4 Wright R-3350 engines with 2 stage super-chargers and anti-detonation injection (ADI) system.

    The ADI system allowed "wet" power (max 3700 BHP) versus dry power (max 3400 BHP), generally for take-offs only, and was limited to a max of 5 minutes use from the individual engine tanks of 10 gallons each. The ADI fluid was 60% methanol and 40% water. The additional power when "wet" did not come directly from the ADI fluid, but from the higher permissible boost from the supercharger (59.5 Hg versus 58.5 Hg) because detonation was suppressed. If ADI wasn't available, maximum dry power used extra fuel to cool the charge.

    Bottom line: ADI injection doesn't increase available power, unless you have a supercharged (or turbocharged) induction system designed to take advantage of it. If your bike isn't detonating under full power conditions, ADI isn't going to help you.

    Different engines may "like" some atmospheric conditions better than others but that's unscientific. Water alone doesn't burn or compress, and air that is holding moisture, has less room for oxygen. Humid air may feel denser, but equally dense dry air will ultimately allow more power to be developed.

    JP

  13. #13
    Small road corner junkie pffog's Avatar
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    Cooler air is slightly more dense, and will MARGINALLY effect power. The water injection systems were effective because the evaporation of the injected fluid, alcohol speeds evaporation, cools the incoming air and makes it denser, not sure fog has the same effect.

    That said, HP is overrated, like the anti loud pipe tee shirt says, imagine what learning to ride your bike will do.....................
    2010 F800GS Full Ohlins package, '04 R1100S Replika
    '01 F650GS Wife's bike
    Maritime Alps and Vosges 2012
    Tuscany and Central Italy 2010

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    I never noticed any difference in power, but I notice a huge difference in smoothness. On the same day, after the temp rises, and the foggishness burns off, my bike doesn't run as smoothly. I am guessing it has to do with the fuel/air mixture somehow - also unscientific.

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    cool morning air

    Once on an early morning jaunt aboard our R100s my riding partner remarked "These airheads just love that cold dense air, don't they?". Well, later I discovered that cold and dense are one thing, damp is something else. All other things being equal, for every 10 degree drop in intake temperature there is a 1% increase in torque: David Vizard "How to build Horsepower" page 11. When colder, there are more molecules of oxygen and with a comparable increase in fuel, more power.

    Water, and sometimes alcohol, if introduced into the combustion chamber will do two things, 1) cool the intake charge and 2) slow detonation.Pre-ignition, pinging (as in high compression or forced induction motors) is overcome by introducing water or alcohol to slow down flame propogation in the cylinder upon ignition of the fuel/air mixture by the spark. So said Luftmeister when selling you a water/alcohol injector for your turbo.

    So I guess with cold damp morning air, there may be a scientific basis for saying the old airheads do run better especially if you are running the 9.5 c/r pistons.

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